Create new connector HTTP APIs that use the new terminology

[mikecote]

This is the first step of #90375, which summarizes the new terminology to use in Kibana alerting. This issue covers the connectors portion, where we use action as the current terminology at this time. This new terminology change includes URL, parameters, body, and response in the new APIs. Don't forget docs.

Actions Plugin Api Paths

Important note: When introducing these new APIs we need to rename all fields in bodies need to be renamed from Camel Case to Snake Case as per our Style Guide. In the code they need to be renamed back to Camel Case.

• POST /api/actions/action => /api/actions/connector
• DELETE /api/actions/action/{id} => /api/actions/connector/{id}
• GET /api/actions => /api/actions/connectors
• GET /api/actions/action/{id} => /api/actions/connector/{id}
• GET /api/actions/list_action_types => /api/actions/list_connector_types
• PUT /api/actions/action/{id} => /api/actions/connector/{id}
• POST /api/actions/action/{id}/_execute => /api/actions/connector/{id}/_execute

For details on the Api migration see the notes under #90375 (comment)

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)