feat: add includeLabels option to release-notes

[jackfrancis]

What type of PR is this?

/kind feature

What this PR does / why we need it:

For monorepo github repositories in the Kubernetes ecosystem that share a common master/main branch, we need a way to differentiate commits in order to use release-notes in a fully automated way.

This PR introduces a user-configurable labels filter that can be used to instruct release-notes "only include commits that originate from PRs w/ one of these labels" in the generated output.

In particular, this would enable SIG Autoscaling to leverage release-notes for the variety of projects under a common repository (e.g., Cluster Autoscaler, Vertical Pod Autoscaling).

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?

feat: add includeLabels option to release-notes

[mboersma]

/lgtm

[jackfrancis]

/assign @puerco

Let me know if this isn't code complete for adding a new release-notes config flag, this is my first PR against this project!

(Also if there's anything additional I should do to advocate for new feature inclusion, happy to...)

[xmudrii]

Thank you for the contribution! Some very nitty comments to match the style with other things, but otherwise LGTM!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: jackfrancis, mboersma
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[jackfrancis]

@xmudrii Thanks for the review!

Tested a local build and it's doing what we want in the kubernetes/autoscaling project:

$ ./release-notes --org kubernetes --repo autoscaler --branch master --repo-path /Users/jackfrancis/go/src/k8s.io/autoscaler/ --start-sha 1959f5f61f6c4b818e668bd52fcd160c0d751fe4 --end-sha b8f910fdf446fba86a4d13991b99749faa764089 --markdown-links true --output notes.md --list-v2 --dependencies=false
WARN No subcommand specified, running "generate"  
INFO Using output format: markdown                
INFO Gathering release notes                      
WARN EXPERIMENTAL IMPLEMENTATION ListReleaseNotesV2 ENABLED 
INFO will stop at 8e7d62b26ef82317ad23b59ead574b4ed0a9e259 
INFO processing release notes for 83 commits      
83 / 83 [--------------------------------------------------------------------------------------------------------------------------------------------------------------------------] 100.00% 20 p/s
INFO Finished gathering release notes in 4.976721166s 
INFO Got 29 release notes, performing rendering   
INFO Release notes written to file: notes.md      
$ ./release-notes --org kubernetes --repo autoscaler --branch master --repo-path /Users/jackfrancis/go/src/k8s.io/autoscaler/ --start-sha 1959f5f61f6c4b818e668bd52fcd160c0d751fe4 --end-sha b8f910fdf446fba86a4d13991b99749faa764089 --markdown-links true --output notes.md --list-v2 --dependencies=false --include-labels "area/cluster-autoscaler"
WARN No subcommand specified, running "generate"  
INFO Using output format: markdown                
INFO Gathering release notes                      
WARN EXPERIMENTAL IMPLEMENTATION ListReleaseNotesV2 ENABLED 
INFO will stop at 8e7d62b26ef82317ad23b59ead574b4ed0a9e259 
INFO processing release notes for 83 commits      
83 / 83 [--------------------------------------------------------------------------------------------------------------------------------------------------------------------------] 100.00% 21 p/s
INFO Finished gathering release notes in 4.4499535s 
INFO Got 16 release notes, performing rendering   
INFO Release notes written to file: notes.md 

First example is without the --include-labels filter (29 results), second example has it (16 results).

FYI @towca @omerap12 @adrianmoisey @elmiko this will help us to better automate releases across CAS/VPA