Make Key Actions Enum - Githubissues

Similar to #363, but for key actions.

All values are available in documentation here: https://www.meilisearch.com/docs/reference/api/keys#actions
Enum should use camelCase (so documents.add = documentsAdd)
User should be able to provide unsupported action to array
Response should be able to handle unsupported actions returned (minus compiler safety)

meilisearch / meilisearch-swift