ci: fix missing tag on containers on git tag pushes

ci: remove cleanup-pr-containers workflow

phase2: add support for overriding feeds host

phase1: simplify feeds host override with SDK cleanup

phase1: apply feeds_host_override to main repository URL

ci: fix workflow_dispatch on PRs by using local context for docker buildx

ci: avoid branch tags on workflow_dispatch

ci: rename OPENWRT_VERSION to BUILDBOT_CONFIG_SHA

ci: add container version tag to BUILDWORKER_DESCRIPTION

ci: centralize BUILDBOT_VERSION in a shared file

ci: add support for testing PR containers

ci: remove very old GitLab bits

docker: fix Dockerfile deprecation warnings

phase1: add support for overriding feeds host

phase2: fix signing steps when only apk_key is defined