Avoid running CI on self-hosted runner when possible

[Kailai-Wang]

Context

We run most of our CI jobs on a self-hosted machine, mostly because we want to push the docker image from there (where the docker credential is already configured)

This is causing a few problems:

• the build is executed sequentially and very slow, especially when multiple PRs are pending
• CI host is shared with other projects, which slows down the build further
• They are not built in a standard env, so any env changes on the host could affect the output

Task

We should try to avoid using self-hosted runner when possible, especially for build & test.
We can leave as it is for other tasks where running on self-hosted runner is absolutely required (e.g. benchmarking, as we need to login to other remote hosts from the CI-host)

Acceptance criteria

• remove all the self-hosted usage in build_and_run_test.yml

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[Kailai-Wang]

Thanks to @geastwood , now DOCKERHUB* env is configured as GH secrets.

[Kailai-Wang]

building docker image takes 20 min on self-hosted runner while on github-runner it takes ~ 1hr.
I think we still need to keep docker-image building on self-hosted runner and do everything else on github runner

[Kailai-Wang]

Currently considering using docker/build-push-action to cache the docker image layers. Will make a few experimental commits and see how it performs.