Add command for inspecting and manipulating node metadata

[aduffeck]

This PR adds a 'ocis decomposedfs metadata' command for inspecting and manipulating node metadata.

CLI:

ocis decomposedfs metadata
NAME:
   ocis decomposedfs metadata - cli tools to inspect and manipulate node metadata

USAGE:
   ocis decomposedfs metadata command [command options] [arguments...]

COMMANDS:
   dump     print the metadata of the given node. String attributes will be enclosed in quotes. Binary attributes will be returned encoded as base64 with their value being prefixed with '0s'.
   get      print a specific attribute of the given node. String attributes will be enclosed in quotes. Binary attributes will be returned encoded as base64 with their value being prefixed with '0s'.
   set      manipulate metadata of the given node. Binary attributes can be given hex encoded (prefix by '0x') or base64 encoded (prefix by '0s').
   help, h  Shows a list of commands or help for one command

OPTIONS:
   --root value, -r value  Path to the decomposedfs
   --node value, -n value  Path to or ID of the node to inspect
   --help, -h              show help

[aduffeck]

Depends on cs3org/reva#3732

[ownclouders]

💥 Acceptance test localApiTests-apiSpaces-ocis failed. Further test are cancelled...

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

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