cache(gha): add timeout attr for cache export/import

[crazy-max]

related to https://github.com/moby/buildkit/actions/runs/8062307240/job/22024437641?pr=4698#step:7:1683 closes #4705

On repositories relying heavily on GitHub Actions Cache backend with BuildKit, it can take more than 5 minutes (current default) for the request to succeed due to GitHub rate limit or if export is quite huge (often sees with mode=max).

This PR adds a timeout attribute for GitHub Actions cache export/import (maybe import is not necessary) so user can specify a custom value if he wants to.

Also increases default timeout to 10 minutes.

If we are not ok with this change, we can just set ignore-error=true in our workflows to avoid failures on this repo, see https://github.com/moby/buildkit/pull/4705

@dvdksn Needs docs follow-up if accepted https://docs.docker.com/build/cache/backends/gha/