* For #5577 - Adds button to add a new search engine

* For #5577 - Adds custom engine store

* For #5577 - Creates a custom SearchEngineProvider

* For #5577 - Gives the ability to delete search engines

* For #5577 - Adds the UI to add a custom search engine

* For #5577 - Adds form to create a custom search engine

* For #5577 - Adds the ability to add a custom search engine

*  For #5577 - Adds the ability to delete custom search engines

* For #5577 - Selects the first element on the add custom search engine screen

* For #5577 - Prevents adding a search engine that already exists

* For #5577 - Styles the add search engine preference

* For #5577 - Makes the name check case-insensitive

* For #5577 - Fix bug where home screen doesnt see new search engines

* For #5577 - Moves Search URL validation to its own type

* For #5577 - Fixes linting errors

* For #5577 - Adds the ability to edit a custom search engine

* For #5577 - Allows the user to edit a serach engine even when it is the last item in the list

* For #5577 - Adds an undo snackbar when deleting a search engine

* For #5577 - Moves all of the strings to be translated

* For #5577 - Fixes bug when deleting your default search engine

* For #5577 - Puts adding search engines behind a feature flag

* For #5577 - Navigate to custom search engine SUMO article when tapping learn more

* For #5577 - Fixes nits

* For #5577 - Uses concept-fetch to validate search string

* For #5577 - Adds string resources for the cannot reach error state