Resolve "Support Spack and others"

### Usage information

Download Spack and setup environment:
```bash
git clone -c feature.manyFiles=true https://github.com/spack/spack.git
. spack/share/spack/setup-env.sh
```
Add GekkoFS Spack repository to Spack:
```bash
spack repo add gekkofs/scripts/spack
```
Check that Spack can find GekkoFS:
```
spack info gekkofs
```
Install GekkoFS (and run optional tests). Check `spack info gekkofs` for available option and versions:
```bash
spack install gekkofs
# for installing tests dependencies and running tests
spack install -v --test=root gekkofs +tests
```
Load GekkoFS into environment:
```
spack load gekkofs
```
If you want to use the latest developer branch of GekkoFS:
```
spack install gekkofs@latest
```
The default is using version 0.9.1 the last stable release.

### TODO

- [x] Base Spack functionality, versions, and configuration support
- [x] Documentation
- [x] Advanced functionality, more detailed configuration support, e.g., Parallax and Prometheus
- [x] More easy way to get path to client library
- [x] Add GekkoFS client wrapper for `LD_PRELOAD`
- [ ] Add final version to main Spack repository if possible. (Not possible right now as it not clear how 3rd party libraries should be treated.





















Closes #58

Closes #58

See merge request !137

Arm Support

This adds ARM support.

It adds a new profile to download the syscall_intercept that supports ARM (fork).
The modifications doesn't use ARM define, as it is not needed, we only need to check if a syscall exists or not.

Closes #244 
We can close !127 also, I think that this merge updates and solves some issues.

Closes #244

See merge request !160

Resolve "Support for (parallel) append operations"

This MR adds (parallel) append support for write operations. There was already some append code available that was run for each `pwrite` when the file size was updated. As a result, parts of strings were serialized and deserialized within RocksDB's merge operation even if not needed. Previously, `open()` was returning `ENOTSUP` when `O_APPEND` was used. When removing this statement, append was not functional due to how size updates and the append case worked. Overall, `gkfs_pwrite()` which first updates the file size and then writes the file was quite messy with unused return values and arguments. Further, the server calculated the updated size without regard on what occurred in the KV store. Therefore, as part of this MR, the entire update size process within `pwrite()` was refactored. 

Parallel appends are achieved by hooking into RocksDB's `Merge Operator` which is triggered at some point (e.g., during `Get()`). Without append being used, the offset is known to the client already and therefore the file size is updated to `offset + count` set in `gkfs_pwrite()`. There is no further coordination required since overlapping offsets are the user's responsibility. The code path for non-append operations was slightly optimized but largely remains the same. 

Append operations are treated differently because it is not clear during a write operation where a process calling `write()` should start writing. Using the EOF information that is loaded during open may be outdated when multiple processes try to append at the same time -> causing a race condition. Since the size update on the daemon is atomic, a process (updating the size before performing a write) can be reserved a corresponding byte interval `[EOF, EOF + count]`. Now, calling `Merge()` on RocksDB does not trigger a Merge operation since multiple Merges are batched before the operation is run. For append, the Merge operation is forced by running `Get()` on RocksDB. The corresponding Merge operation then responds the starting write offset to the updating size process. Therefore, appends are more expensive than non-appends.

Lastly, some missing documentation was added.

As reported, this MR adds support for the DASI application, used in IO-SEA.

Note: This MR does not consider failing writes which would require us to collapse a reserved interval and tie up the hole in the file. 

Closes #254
Closes #12

Closes #12 and #254

See merge request !164

Resolve "Issue to fetch nlohmann_json"

Closes #264

Closes #264

See merge request !167

Improve cmake

This MR improves the current CMake scripts in the following manner:

- Dependency management is now handled more consistently: system dependencies are found using `find_package()`, whereas source-only dependencies are found using `include_from_source()`. This new function integrates a dependency provided its source code is available. If it's not, it will try to download it from its git repository if it was defined.
- All external dependencies are now searched for in the top-level `CMakeLists.txt`.
- More consistent use of targets (we are closer to 100% modern CMake).
- Adds the `gkfs_feature_summary()` to allow printing a summary of all GekkoFS configuration options and their values.
- Moves all option definitions to `CMake/gfks-options.cmake`, so that the top-level `CMakeLists.txt` is cleaner. It also defines the `gkfs_define_option()` and `gkfs_define_variable()` functions to integrate the definition of options/variables with the automated reporting provided by `gkfs_feature_summary()`.

It also fixes #249.

Closes #211

Closes #211 and #249

See merge request !143

The function include_from_source() now checks if the source directory
for a external dependency is empty. If so, it will provide instructions
for the user to solve the issue (such as properly initializing
submodules).

Until #250 is fixed