refs TryGhost/Team#2904
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### <samp>🤖 Generated by Copilot at b3f5423</samp>
This pull request adds support for multiple formats of snippet content,
especially the `lexical` format, to the Ghost CMS. It modifies the
snippets API, model, and test files to handle the format conversion,
filtering, and serialization of snippets.
- this cleans up all imports or variables that aren't currently being used
- this really helps keep the tests clean by only allowing what is needed
- I've left `should` as an exemption for now because we need to clean up
how it is used
refs https://github.com/TryGhost/Toolbox/issues/522
- Having simpler method signature makes it easier to use it in different context - needed for changes in public resource repository
- TLDR of the changes - reduced parameter 'frame.options' -> 'options'
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/363
- this API framework is standalone and should be pulled out into a
separate package so we can define its boundaries more clearly, and
promote better testing of smaller parts
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
