* Server side changes

- removed console_legacy plugin!
- added new es_config endpoint that returns server side es config
  at the moment this is just the first value in hosts
- Slight refactor to how routes are registered to bring them more
  in line with other ES UI plugins

* Client side update

- Updated the client to not get es host from injected metadata.
  Instead use the new endpoint created server side that returns
  this value
- Added a small README.md regarding the hooks lib and need to
  refactor use of jQuery in console
- Write code to init the es host value on the client once at start
  up in a non-blocking way. If this fails we just use the default
  value of http://localhost:9200 as this powers non-essential
  console functionality (i.e., copy as cURL).

* fix type issue and jest tests

* fix another type issue

* simplify proxy assignment in proxy handler mock

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>