Skip deleted namespaces from a migration schedule

[Rohit-PX]

Signed-off-by: Rohit-PX rkulkarni@purestorage.com

What type of PR is this?
improvement

What this PR does / why we need it:

• In a migration schedule, if a namespace that is present in the migration schedule is deleted, then we throw an error and fail subsequently triggered migrations
• This results in stoppage of migrations for namespaces that are still present and which the user would like to be migrated

Improvement can be as below:

• Even if a deleted namespace is present in a migration schedule, add warning messages but proceed with migration of other namespaces.
• Add flag in the migration schedule spec to proceed with migrations for other namespaces even if some namespaces are deleted.

Does this PR change a user-facing CRD or CLI?:

Is a release note needed?:

Issue:  https://portworx.atlassian.net/browse/PWX-23459
User Impact: 
Namespaces that are deleted but are present in the migration schedule namespaces list those migrations were being marked as failed. 
Resolution:
Migration schedule spec will have a new bool field: SkipDeletedNamespaces that will determine if migrations are to be marked as failed in case some namespaces are deleted.

Does this change need to be cherry-picked to a release branch?:
2.11

[cnbu-jenkins]

Can one of the admins verify this patch?

[lpitstickpstg]

Does this default to False?
The other bools here are *bool

[Rohit-PX]

Yes it will default to false, but fixed it to maintain code standards.