Entity search - take one

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

Description

This PR adds entity (item) search to the Management API. The "global" search known from V13 will be replaced with individual search endpoints that can be utilized by the client in a mix-and-match fashion.

Note that this is the first take on entity search, to get the ball rolling on the client implementation. The document, media and member search endpoints will be updated later on to use Examine for searching rather that the entity service. At the same time, user start nodes will be honoured by those search endpoints.

Testing this PR

1. Ensure that all search endpoints return results as expected, matching entities by name (partial match/contains) or item key (exact match).
2. Verify that the search endpoints return no results when searching for something that is not there.

[Zeegaan]

Works like a charm 🚀