Add read-only config option

[DL6ER]

What does this implement/fix?

Add new misc.readOnly config option to force the configuration to be read-only. It can only be modified through the config file but neither the API nor the CLI as long as read-only mode is enabled.

Related issue or feature (if applicable): https://discourse.pi-hole.net/t/support-writing-to-pihole-toml-directly/70522/

Pull request in docs with documentation (if applicable): N/A

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• [x] The code change is tested and works locally.
• [x] I based my code and PRs against the repositories developmental branch.
• [x] I signed off all commits. Pi-hole enforces the DCO for all contributions
• [x] I signed all my commits. Pi-hole requires signatures to verify authorship
• [x] I have read the above and my PR is ready for review.

[github-actions[bot]]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions[bot]]

Conflicts have been resolved.

[DL6ER]

Has been confirmed working by original requestor on Discourse

[DL6ER]

Thank you, this was some very good review hint! The issue was that we skipped recomputing the checksum in read-only mode and, hence, FTL did not realize that the file actually changed once you went back from false -> true. However, this bug was only triggered if you have changed other settings before this, effectively hiding it from my tests where I have set misc.readOnly = true as the first thing during testing.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/support-writing-to-pihole-toml-directly/70522/11