feat: add actions API in client

[j33ty]

Add new Actions API implementation: https://www.sanity.io/docs/http-actions

Methods implemented:

1. create: A create action creates a new draft document.
2. replaceDraft: A replaceDraft action replaces an existing draft document.
3. edit: An edit action is used to modify an existing draft document. It applies the given patch to the document referenced by draftId.
4. delete: A delete action is used to delete the published version of a document and optionally some (likely all known) draft versions.
5. discard: A discard action is used to delete the draft version of a document.
6. publish: A publish action is used to publish a draft document. If a published version of the document already exists this is replaced by the current draft document.
7. unpublish: An unpublish action is used to retract a published document. If there is no draft version then this is created from the published version.

[bjoerge]

Great work, Radhe – would love to see some unit tests here as well, if possible.

See also suggestion re: unused file below.

[stipsan]

@j33ty quick heads up, I changed the PR title so it uses semantic prefixing. I noticed you use them for the commits 👍 We usually have them in PR titles as well since "squash & merge" is frequently used, and ensures that regardless of merge method the new version that will be published, and the changelog entries, are correct :)

[rneatherway]

All my comments are addressed. I'll defer to @bjoerge or @stipsan for final review.

[stipsan]

All good from my perspective 👍 I didn't enable auto merge so that @bjoerge has the opportunity to do the final approval ☺️