text: Title: [event log] restructure route paths to avoid path parameters at "beginning" of the urls
  Body: While reviewing PR https://github.com/elastic/kibana/pull/89681, I happened to notice that are URLs are not structured that great.
  
  ```js
  const BASE_EVENT_LOG_API_PATH = "/api/event_log"
  ```
  
  https://github.com/elastic/kibana/blob/b058f7852b74fd22f396c367dc47cf4a526b4daa/x-pack/plugins/event_log/server/routes/find.ts#L25-L27
  
  https://github.com/elastic/kibana/blob/b058f7852b74fd22f396c367dc47cf4a526b4daa/x-pack/plugins/event_log/server/routes/find_by_ids.ts#L29-L31
  
  (new API in PR, shaped the same as others)
  
  https://github.com/elastic/kibana/blob/53d7f763ae684dfd002c1072ebec18ac022180e2/x-pack/plugins/event_log/server/routes/get_events_summary_by_saved_object_ids.ts#L47-L49
  
  Two problems:
  
  - we've now made the path segment after `/api/event_log` always have to be a `type` value - since it could be anything, we can't ever create a fixed path like `/api/event_log/_do_something`, since `_do_something` could be a SO type
  - we may want to have APIs that work over multiple types, but now we can't, since you have to always have a single type as the path segment - I guess you could pass one in on the path, and others via query string, but that's awkward
  
  Seems like we need to reshape these to allow for more URL patterns in the event log in the future.
  