[ILM] Add index templates to "add policy" modal in policies table (#7…

…7077)

* [ILM] Add index templates to "add policy" modal in policies table

* [ILM] Change select to a combobox in 'add policy' modal in policies table

* [ILM] Add not found message to "add policy to template" modal

* [ILM] Fix api integration test

* [ILM] Fix type check error

* [ILM] Add PR review suggestions

* [ILM] Fix type check error

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