Use DockerHub credentials

[jemrobinson]

✅ Checklist

• You have given your pull request a meaningful title (e.g. Enable foobar integration rather than 515 foobar).
• You are targeting the appropriate branch. If you're not certain which one this is, it should be develop.
• Your branch is up-to-date with the target branch (it probably was when you started, but it may have changed since then).

🚦 Depends on

⤴️ Summary

Use DockerHub credential from SREConfig to pull images from dockerhub.

🌂 Related issues

Closes #1984

🔬 Tests

Tested on a fresh SRE deployment

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
data_safe_haven/config
config_sections.py
sre_config.py
data_safe_haven/infrastructure/common
__init__.py
dockerhub_credentials.py
data_safe_haven/infrastructure/programs
declarative_sre.py					80
data_safe_haven/infrastructure/programs/sre
dns_server.py					36
gitea_server.py					55
hedgedoc_server.py					57
identity.py					43
remote_desktop.py					65
software_repositories.py					44
user_services.py					55
data_safe_haven/validators
validators.py
Project Total

This report was generated by python-coverage-comment-action

[JimMadge]

LGTM 🎉