[BACKPORT][v1.5.6][BUG] Longhorn can no longer create XFS volumes smaller than 300 MiB

[github-actions]

backport #8488

[longhorn-io-github-bot]

Pre Ready-For-Testing Checklist

• Where is the reproduce steps/test steps documented?
  The reproduce steps/test steps are at: Refuse to create an XFS volume smaller than 300 MiB longhorn-manager#2785 (comment).

• Is there a workaround for the issue? If so, where is it documented?
  We haven't released code affected by this issue. If we accidentally did, users could just not create Longhorn PVs with fsType: xfs for volumes smaller than 300 MiB.

• Does the PR include the explanation for the fix or the feature?

• Have the backend code been merged (Manager, Engine, Instance Manager, BackupStore etc) (including backport-needed/*)?
  The PR is at: Refuse to create an XFS volume smaller than 300 MiB (backport #2785) longhorn-manager#2802.

• If labeled: require/doc Has the necessary document PR submitted or merged (including backport-needed/*)?
  The documentation issue/PR is at: Document minimum XFS volume size backport website#917.