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:

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

[github-actions]

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

[github-actions]

Conflicts have been resolved.

[DL6ER]

Has been confirmed working by original requestor on Discourse

[yubiuser]

I tried it and setting this option to trueworks as expected. However, setting it back to false needs a manual FTL restart before the change applied. It seems from the logging, FTL stoppend watching the file for changes and therefor does not realize that readOnly is now back to default false

[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