Remove sock files on nginx startup

[ciarams87]

Proposed changes

Problem: NGF Pod cannot recover if NGINX master process fails without cleaning up

Solution: Update the nginx Dockerfile CMD to clean up sock files on start-up

Testing: Followed the repro steps in the bug and confirmed that the pod successfully recovers after killing the NGINX master process

Closes #1108

Checklist

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• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

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please add a brief note that summarizes the change.

Fixed issue where NGF Pod cannot recover if NGINX master process fails without cleaning up

[sjberman]

Test needs to be updated to remove the Skip(): #1108 (comment)

[kate-osborn]

LGTM once the tests are passing. Not sure what's causing the intermittent failure