refs https://github.com/TryGhost/Ghost/pull/15375
- we currently pass all properties for the `tags` property of a
`page`/`post` body down further into Ghost, which is causing issues
because it's handling properties it doesn't expect
- this is showing up because it's triggering save history events for
tags when a post is edited
- this commit introduces a clean util which has an allowlist of
properties allows on tag relations
- this list was taken from the schema: 128f8fb006/packages/admin-api-schema/lib/schemas/posts.json (L214-L227)
refs https://github.com/TryGhost/Toolbox/issues/354
- this commit turns the Ghost repo into a monorepo so we can bring our
internal packages back in, which makes life easier when working on
Ghost
