Add --or-selector for backup and restore command

[nilesh-akhade]

Thank you for contributing to Velero!

Please add a summary of your change

Add 'orLabelSelector' that allows selecting resources matching any one of the label selectors.

With the current implementation of the --selector, it is not possible to select resources that have any one of the labels, app=nginx or foo=bar. This is because the selector, app=nginx,foo=bar will expect both the labels on the resource.

Selecting resources that have any one of the labels is already supported by the Restore and Backup CRDs, through orLabelSelectors: https://velero.io/docs/v1.11/api-types/restore/. This PR adds --or-selector to achieve the same thing using velero cli.

# syntax
velero backup create <backup-name> --or-selector "<label-selector1> or <label-selector2> or ..."

# example 1
velero restore create restore-prod --from-backup=prod-backup --or-selector "env in (prod,production) or environment in (prod,production)"

# example 2
velero backup create backup1 --or-selector "foo=bar or baz=qux"

# example 3
app in (web,nginx) or foo in (bar,baz)
# selects apps that have any one of the labels app=web, app=nginx, foo=bar, foo=baz

Does your change fix a particular issue?

Fixes #5679

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• Updated the corresponding documentation in site/content/docs/main.

[mateusoliveira43]

Looking this docs, couldn't we achieve the same result using the --selector flag with in?

Ex.: Do these commands produce the same result?

• velero backup create nginx-backup --selector "app in (nginx,my-nginx,nginx-example)"
• velero backup create nginx-backup --or-selector "app=nginx|app=my-nginx|app=nginx-example"

Did not try every possibility, but maybe this PR can be achieve only adding examples to the docs with different scenarios (and updating help description of --selector flag in CLI)

[mateusoliveira43]

But I think the usage from the docs is limited. For example, if I have 2 (or more) different labels (KEYs), I can't do an OR with them ("Similarly the comma separator acts as an AND operator.")

[sseago]

@mateusoliveira43 yes -- that's the sort of scenario the or selector was added for:
velero backup create nginx-backup --or-selector "app=nginx|foo=bar"

[nilesh-akhade]

If resources to be backed up are labeled either env=prod or environment=production, then we cannot use --selector env=prod,environment=production. But we can use --or-selector "env=prod|environment=production"

I have updated the PR to include examples and explanations.

[nilesh-akhade]

I have modified the syntax a little bit. The or keyword can be used in place of | pipe symbol.

[codecov-commenter]

Codecov Report

Merging #6475 (d9a7e2b) into main (f234dd6) will decrease coverage by 0.03%.
The diff coverage is 48.00%.

@@            Coverage Diff             @@
##             main    #6475      +/-   ##
==========================================
- Coverage   60.28%   60.26%   -0.03%     
==========================================
  Files         238      239       +1     
  Lines       25256    25306      +50     
==========================================
+ Hits        15226    15250      +24     
- Misses       8976     8998      +22     
- Partials     1054     1058       +4     

Impacted Files	Coverage Δ
pkg/cmd/util/output/restore_describer.go	31.52% <0.00%> (-1.23%)	⬇️
pkg/cmd/cli/backup/create.go	66.41% <40.00%> (-0.51%)	⬇️
pkg/cmd/cli/restore/create.go	61.05% <40.00%> (-0.38%)	⬇️
pkg/cmd/util/output/backup_describer.go	55.49% <45.45%> (-0.21%)	⬇️
pkg/cmd/util/flag/orlabelselector.go	83.33% <83.33%> (ø)

[reasonerjt]

Since it's passed the v1.12 FC milestone, and this does not introduce big changes to the API, we'll target this one to the patch v1.12.1

[draghuram]

Now that 1.12 is released, can this PR be merged?