Create Instance

[MHHukiewitz]

Adds two new functions:
-aleph instance create: Creates a new instance
-aleph instance delete: Deletes/Forgets an instance

[github-actions]

This PR introduces a new command instance with multiple subcommands for managing instances on the Aleph.im network, such as creating and deleting instances.

• Adding a new file src/aleph_client/commands/instance.py with the implementation of the instance command and its subcommands.
• Updating src/aleph_client/conf.py to include new default values for rootfs settings.
• Adding help strings for the new command and its subcommands in src/aleph_client/commands/help_strings.py.
• Refactoring volume parsing in src/aleph_client/commands/utils.py

The complexity of this PR is rated as 'BLACK' due to the extensive changes it introduces, which may have a high potential for introducing bugs or requiring deep understanding of the project architecture. Only experienced developers should review this PR.

Has been downgraded to RED, due to the previously mistaken assumption that creating volumes is a new feature in this PR

[1yam]

LGTM