fix: docker-support.md

[cs168898]

Fixed the broken Docker file link that was mentioned in nginx/agent#1087 (Issue #1087)
NGINX Documentation Issue number: #1051

Proposed changes

The pull request fixes the URL link in the NGINX Agent documentation Dockerfile URL to the updated URL.

I changed it through clicking the 'edit page' button located at the bottom of the documentation page then editing it in the forked version before committing it and creating a PR.

The changes will not affect anything else but it might be affected in the future if the structure of the NGINX Agent repository changes again.

Additional Context:
I am new to the world of contributing, please let me know if I am doing anything wrongly, thank you!

Checklist

Before sharing this pull request, I completed the following checklist:

• I read the Contributing guidelines
• My branch adheres to the Git conventions
• My content changes adhere to the F5 NGINX Documentation style guide
• If my changes involve potentially sensitive information¹, I have assessed the possible impact
• I have waited to ensure my changes pass tests, and addressed any discovered issues

Footnotes

1. Potentially sensitive information includes personally identify information (PII), authentication credentials, and live URLs. Refer to the style guide for guidance about placeholder content. ↩

[github-actions]

✅ All required contributors have signed the F5 CLA for this PR. Thank you!
_{Posted by the CLA Assistant Lite bot.}

[cs168898]

I have hereby read the F5 CLA and agree to its terms

[mjang]

I have a 2nd implied approval internally, so I'm proceeding with merge.

[mjang]

thank you @cs168898 so much for your contribution!