[gha/docker] build with branch name; also cleanup

[rustielin]

Builds off of special branches like main get image tags now in the form:

• <branch_name>
• <branch_name>_<git_sha>

This is useful for Forge, which by default should use the latest stable processors version. Currently it's pinned to some recent commit hash

Also general cleanup of branch push triggers

Test plan

Canary runs on push to PR branch. It pushes all the expected tags

INFO[0237] Pushing image to us-docker.pkg.dev/aptos-registry/docker/indexer-client-examples/rust:dbd773c4d0c6c4bac21bc210dadd87eb0b11863c 
INFO[0240] Pushed us-docker.pkg.dev/aptos-registry/docker/indexer-client-examples/rust@sha256:6776a413b25dd4ec6a632a34719376ff36366e192f2999c4704d2b3200431481 
INFO[0240] Pushing image to us-docker.pkg.dev/aptos-registry/docker/indexer-client-examples/rust:rustielin-branch-prefix-build 
INFO[0241] Pushed us-docker.pkg.dev/aptos-registry/docker/indexer-client-examples/rust@sha256:6776a413b25dd4ec6a632a34719376ff36366e192f2999c4704d2b3200431481 
INFO[0241] Pushing image to us-docker.pkg.dev/aptos-registry/docker/indexer-client-examples/rust:rustielin-branch-prefix-build_dbd773c4d0c6c4bac21bc210dadd87eb0b11863c 
INFO[0242] Pushed us-docker.pkg.dev/aptos-registry/docker/indexer-client-examples/rust@sha256:6776a413b25dd4ec6a632a34719376ff36366e[192](https://github.com/aptos-labs/aptos-indexer-processors/actions/runs/11168000083/job/31045425474?pr=538#step:5:193)f2999c4704d2b3200431481

And it's in GAR

[igor-aptos]

how do you define: "latest stable processors version" ?

is that just latest built from main, or something else?

[rustielin]

For now it's just the latest built from main. Since main is where we cut our releases from for processors, and there's no branching strategy for release, this is generally assumed safe.

For tests we could also consider using the latest release version (by tag)