feat: Reintroduce crowdin synchronization.

[IMB11]

This is a continuation of @brawaru's previous pull request before the monorepo (modrinth/knossos#1640) with the main change being it only runs on the main branch, rather than using Crowdin's branching functionality to have multiple branches of sources, which we wouldn't use anymore.

Thank you @brawaru!

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Prerequisites

• Delete all sources from the Crowdin project (whilst keeping the translation memory!)
• Make sure there are no github-related integrations in the integrations tab.
• Create a fine-grained access token for the "Modrinth Bot" github account with the following permissions, placing it in the CROWDIN_GH_TOKEN repository environment secret;
  • contents: write
  • pull-requests: write
• Copy the https://crowdin.com/project/modrinth project ID into the CROWDIN_PROJECT_ID repository variable.
• Create an access token on the "Modrinth" crowdin account with all scopes, and place the token into CROWDIN_PERSONAL_TOKEN repo secret.
• Modify the pull request description template in .github as needed (probably wont need any changes honestly)
• Merge the PR.
• The push workflow should run and push the new sources to Crowdin.
• (optional) Pre-translate using translation memory.

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The first pull request made by the CI will be large as it has to populate the initial locale files with {}, after that it should be pretty small and review-able.

[IMB11]

After #4025 is merged, we can add it to the crowdin.yml for the moderation package. Can be done in a different PR though.

[brawaru]

If you manually move the existing files on Crowdin to expected locations before first running this workflow, you won't have to lose any translations and force translators to restore translations by hand from translation memory! :)

That is,

1. Rename [modrinth.knossos] master to [modrinth.code] main
2. Create web subfolder under [modrinth.code] main
3. Select all files in the root of [modrinth.code] main and move them to web
4. Create ui subfolder under [modrinth.code] main
5. Drag index.json from [modrinth.omorphia] master to that ui folder