Test BIAv2 impl

[sseago]

This provides a test implementation of a v2 BackupItemAction plugin. It is fully functional (built on top of #5271), but the added interface method is for testing purposes only. This should not be merged as-is.

I've also created a velero-plugin-example PR which adds a test v2 plugin to test with this.

Does your change fix a particular issue?

Fixes #(issue)

Please indicate you've done the following:

• [x ] 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.

[sseago]

vmware-tanzu/velero-plugin-example#66 is a plugin image with a v1 and v2 BIA plugin for testing.

[codecov-commenter]

Codecov Report

Merging #5278 (328a699) into main (1e138af) will decrease coverage by 0.32%.
The diff coverage is 28.83%.

@@            Coverage Diff             @@
##             main    #5278      +/-   ##
==========================================
- Coverage   40.82%   40.49%   -0.33%     
==========================================
  Files         234      238       +4     
  Lines       20269    20584     +315     
==========================================
+ Hits         8274     8335      +61     
- Misses      11393    11641     +248     
- Partials      602      608       +6     

Impacted Files	Coverage Δ
internal/velero/serverstatusrequest.go	0.00% <0.00%> (ø)
pkg/backup/request.go	100.00% <ø> (ø)
pkg/cmd/server/server.go	6.59% <0.00%> (ø)
pkg/controller/server_status_request_controller.go	66.15% <ø> (ø)
pkg/plugin/clientmgmt/process/logrus_adapter.go	17.56% <ø> (ø)
...g/plugin/clientmgmt/process/restartable_process.go	0.00% <0.00%> (ø)
pkg/plugin/framework/action_resolver.go	5.75% <0.00%> (-1.15%)	⬇️
pkg/plugin/framework/backup_item_action.go	0.00% <0.00%> (ø)
pkg/plugin/framework/backup_item_action_client.go	0.00% <0.00%> (ø)
...ramework/backupitemaction/v2/backup_item_action.go	0.00% <0.00%> (ø)
... and 51 more

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