Authenticate against Docker Hub to prevent rate limiting in CI

[pmalek]

Problem statement

CI is hitting Docker Hub quota when pulling images in tests.

E.g. https://github.com/Kong/go-kong/actions/runs/10248803126/job/28350853450?pr=455

Run make setup-kong-ee
bash .ci/setup_kong_ee.sh
6524b92b9ad345147fbd576ac[11](https://github.com/Kong/go-kong/actions/runs/10248803126/job/28350853450?pr=455#step:5:12)7a875020190e86ad19e614d85197c0c5e19fa
Unable to find image 'postgres:9.6' locally
9.6: Pulling from library/postgres
docker: toomanyrequests: You have reached your pull rate limit. You may increase the limit by authenticating and upgrading: https://www.docker.com/increase-rate-limit.
See 'docker run --help'.
make: *** [Makefile:54: setup-kong-ee] Error [12](https://github.com/Kong/go-kong/actions/runs/10248803126/job/28350853450?pr=455#step:5:13)5

Proposed solution

Authenticate with Docker Hub using a token in CI.

Acceptance criteria

• CI authenticates with Docker Hub and uses a higher quota for pulling images