Github: Update Docker Login Credentials To Use Token

[steelhead31]

Fixes #3211

Update docker credentials to use PAT, but disable push on merge, due to replacement with docker multiarch jenkins job. Code left to enable easy re-enablement if required.

The docker push on merge has also been disabled, due to the relocation of the centos6 docker push to the jenkins job as per this PR: #3296

Checklist

• commit message has one of the standard prefixes
• VPC/QPC not applicable for this PR

[Haroon-Khel]

I am also in favour of the image push being in Jenkins instead of github workflow, since the Jenkins job is triggered everytime a pr is merged anyway. No need to push the same image twice

[sxa]

We could do a one-off run with push: true to verify that the functionality works as expected, but I'm ok for this to go in regardless since we're switching to using the jenkins job like we do for the other ones.

Ref: https://github.com/docker/login-action/blob/master/README.md#docker-hub (Tokens seem valid in the password field)
Ref: #3296
Also noting that with these changes we should update https://github.com/adoptium/infrastructure/blob/master/FAQ.md#what-about-the-builds-that-use-the-dockerbuild-tag which talks about where the various images are built