Warn if config folder misses original image configs or files differ

[flortsch]

Implements a check in the Docker entrypoint that compares the special config files of this Docker image with the config files of the user folder. It prints a warning if those config files are missing or they differ from the original Docker image config files. This is a first step, as suggested by @joshtrichards in #1533. In the long run, these files should be treated as special config files not to be messed with by the user, and they should be copied over into the user config folder on every update.

[joshtrichards]

Thanks @flortsch!

I'm thinking we should include a new paragraph in the README to refer people to with questions about what is going on here / help them know what they should do. Based on experience with the setup warnings in Nextcloud's Admin Overview, many people pay a lot of attention to these things and get frustrated if they're not able to remedy warnings (understandable reaction + remedying this is the goal!).

Ideally we include that in this PR, but it can also be in an immediately following one if you'd prefer to keep separate.

[flortsch]

Hey @joshtrichards! Sound good. I can extend the PR with a section in the readme and a link to it in the console output. Since you mentioned warnings in the Nextcloud admin overview: is it possible to generate such UI warnings in the entrypoint script? I think that warnings in the UI would be a nice addition to the console output which can often be overlooked.

[flortsch]

@joshtrichards Please check if the text and link is ok. I updated the README and added a link in the docker-entrypoint echo statement. Also, I inlined your last text feedback.

[joshtrichards]

Since you mentioned warnings in the Nextcloud admin overview: is it possible to generate such UI warnings in the entrypoint script? I think that warnings in the UI would be a nice addition to the console output which can often be overlooked.

Not currently.

[joshtrichards]

Finally got a chance to test this a bit. Made some proposed adjustments. Let me know what you think.

[flortsch]

Hey @joshtrichards! I included your suggestions. Only fixed the formatting and the uninitialized variable access. Tested locally with docker-compose (fresh start + changes in existing container/volume). Missing or changed image-specific files trigger the warning & file listing. Custom config files don't trigger anything. Commits squashed and rebased on latest master.