Cache our docker intermediate layer to speedup builds

[viceice]

We should use the caching feature of docker buildx to reuse build layers which do not have changes.

To get started we need

• [x] create new docker hub repo, eg renovate/testing
• [x] create new docker hub deploy account, eg renovatebot
• [x] add new account and @ViceIce with permissions to push/delete
• [x] generate a token for that new account, to be put into github actions

After these steps we can enable build caching in our github workflows

• [ ] add renovaterelease account with permissions to push/delete to renovate/renovate docker repo
• [ ] replace workflow variable DOCKER_REPO with renovate/renovate https://github.com/renovatebot/renovate/blob/a3614f8bbe0b02574662743e8794567407287e5f/.github/workflows/dockerimages.yml#L12-L13

when we want to start to deploy release docker images

• [ ] replace workflow variable DOCKER_REPO with renovate/renovate https://github.com/renovatebot/renovate/blob/a3614f8bbe0b02574662743e8794567407287e5f/.github/workflows/release.yml#L10-L11

[rarkins]

New docker hub repo: renovate/cache-test

New docker hub deploy account: renovaterelease

Added both the new account and kriese with read-write team permissions to renovate/cache-test

Added Docker Hub user renovaterelease access token into Actions secret DOCKER_RENOVATERELEASE_TOKEN

[viceice]

refactored the docker workflows. Now we can merge to master and test.

If it is working fine we need more steps to do

[rarkins]

@ViceIce can this now be closed?

[viceice]

no, i will try to use github file cache, so we don't need to push the cache to dockerhub