feat: [WD-18264] CMS fields for storage pool source

[Kxiru]

Done

• Added intermediary StoragePoolClusteredSourceSelector file + a ClusterSpecificInput component.
• Added functionality to create storage pool source fields for specific cluster members.

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @mas-who or @edlerd for access.
   • With a local copy of this branch, build and run as described in the docs.
2. Perform the following QA steps:
   • Within a clustered environment, navigate to the Create a storage pool page, and attempt to create a storage pool with a ZFS, LVM or Directory driver. (Directory is less prone to error and empty directories can be made for testing purposes by creating them in the terminal of the cluster node).
   • With a storage pool successfully created, navigate to it's configuration page and verify that
     • The page defaults to the correct setting (global source or single clusters sources)
     • The previously input sources persist.

Screenshots

[webteam-app]

Demo

Jenkins

demos.haus

[edlerd]

Good progress, some comments on the code below.

[edlerd]

It is fully functional now, good progress. I found some QA and code issues below.

[mas-who]

Good work! Some code comments so far

[mas-who]

@Kxiru I realise some of my comments may have overlapped with comments from @edlerd . Please resolve the issues if it's already addressed by your responses to @edlerd

[edlerd]

QA and code LGTM, tiny non-blocking nitpick on the class naming, good to go as is.