feat: remove assets from repository (see #4759) (#5133)

BREAKING CHANGE: The assets are no longer embedded in source code: javascript, css, font files. Run `yarn install` then `yarn run production` to recreate them from sources, or download a [release file](https://github.com/monicahq/monica/releases) that contains compiled files.

BREAKING CHANGE: For Heroku users: You'll have to manually go to `Settings` > `Buildpacks` and add buildpack: `nodejs`. See [this doc](https://github.com/monicahq/monica/blob/master/docs/installation/providers/heroku.md#update-from-2x-to-3x).

BREAKING CHANGE: See more information about how to install a Monica instance [here](https://github.com/monicahq/monica/tree/master/docs/installation).