Implement rename, renameat, renameat2

Added new rcp "insert_node" to insert new metadentry into the metadata DB.
This call differs from the "mk_node" because it will insert the metadata
received from the caller instead of generating them assuming that they
have been generated previously.

It can be used to move entries between metadata nodes

add checks for directory existance before to remove it

remove_node RPC can now be used to remove only the metadentry from the
metadata DB without touching the relative data in the ChunkStorage.

 - ChunkStorage now use file ID to organize chunks and locate them
 - all the data rpc now accepts the file ID instead of the file path

The OpenFile and Metadata class have now a fuid field that is a unique file identifier. The fuid is generated by a metadata daemon when the new node is created.

Remove the optional inode support

See merge request zdvresearch_bsc/adafs!98

Refactor adafs internal read/write funciton

See merge request zdvresearch_bsc/adafs!97

the functionality wasn't used at all and it will be implemented later
with a different approach

 - Added adafs_pwrite and adafs_pread functions:
        they accept an OpenFile pointer instead of a fd so that can be
        called by function that already accessed the OpenFileMap.

 - Moved the writev function into internal adafs functions.

 - Added internal adafs_write function:
        instead messing up with the file position at the interception
        layer, we can use this internal function that hides the update of the
        file position two.

various metadata related improvements

See merge request zdvresearch_bsc/adafs!96

Instead of passing only the mode as paramenter, we now pass an entire
Metadata object in such a way that the parameter can be configured at
compile time. For instace if we support symlinks we would like also to
pass the target path

Can be used to retrieve the Metadata object for a named path

In several places the adafs_stat function have been replaced with this
new adafs_metadata. This allowed to avoid the construnction of the
additional `struct stat`.