Add checks to verify DB migrations are actually done.

[JBassett]

Summary

With any luck this will fail builds if migrations are missing or incorrectly updating existing migrations.

Screenshots

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Link to pull request in Documentation repository

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Any other notes

[jpelgrom]

Wouldn't it be better to run these checks as soon as possible (modified almost immediately, missing after building)? I can't think of a reason to build or archive the app if the action is going to fail because of changed or missing DB schema files.

[JBassett]

So we at least need the second one after the build to check to see if a change was made to code that would affect the schema. It would manifest as an uncommitted change. And since that one needs to be done after a build I just put both after the build.

[jpelgrom]

Another scenario which isn't working: bumped the database version but didn't add the schema file to git. Example PR: https://github.com/jpelgrom/home-assistant-android/pull/4

The existing checks only seem to consider changes to existing files or staged changes, but after Gradle is done building new files aren't staged

[jpelgrom]

@JBassett Is it OK if I have a go at fixing/implementing this? There haven't been a lot of database changes recently but this is still nice to have

[JBassett]

@jpelgrom have at it, life/work has kept me on a review only basis for a while now. Thanks!