Docker image: Add source code reference label

[mfrister]

What this PR does / why we need it:

Add a opencontainers-standardized label (source) to the Docker image, referencing the ingress-nginx GitHub repository.

This allows tools that automate component updates (in our case Renovate Bot) to automatically find the source repository for the Docker image and extract release notes from there. Renovate Bot can include the relevant release notes automatically in a merge request changing the component version.

In renovatebot/renovate#3753, Renovate added the label for their own Docker image.

[k8s-ci-robot]

Hi @mfrister. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[cmluciano]

Will defer to @aledbf on this one

[aledbf]

@mfrister I don't see any issues adding this label but I think we should add more labels than "source", like

LABEL org.opencontainers.image.title='NGINX Ingress Controller for Kubernetes'
LABEL org.opencontainers.image.documentation='https://kubernetes.github.io/ingress-nginx/'
LABEL org.opencontainers.image.source="https://github.com/kubernetes/ingress-nginx"
LABEL org.opencontainers.image.vendor='The Kubernetes Authors'
LABEL org.opencontainers.image.licenses='Apache-2.0'
LABEL org.opencontainers.image.version='0.26.1'

WDYT?

[mfrister]

@aledbf Good idea. Added the labels you suggested, using the TAG available in the Makefile as version label.

[aledbf]

/ok-to-test

[codecov-io]

Codecov Report

Merging #4747 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4747      +/-   ##
==========================================
+ Coverage    58.6%   58.62%   +0.01%     
==========================================
  Files          88       88              
  Lines        6743     6743              
==========================================
+ Hits         3952     3953       +1     
+ Misses       2355     2353       -2     
- Partials      436      437       +1

Impacted Files	Coverage Δ
internal/watch/file_watcher.go	84.61% <0%> (+3.84%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d1eea79...dea9c40. Read the comment docs.

[aledbf]

/lgtm

[aledbf]

@mfrister thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, mfrister

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [aledbf]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment