Community Edition should have a HASH Join warning message

Summary: HASH join in N1QL is not supported in Community Edition. Currently, it falls back to Nested Loop silently, which could be frustrating.

Repro:

1. Open up Query Workbench in Community Edition (I used build 2473)
2. Enter a query that uses HASH join, for instance: SELECT l.name AS landmarkName, h.name AS hotelName, l.email AS landmarkEmail, h.email AS hotelEmail
   FROM `travel-sample` l
   INNER JOIN `travel-sample` h USE HASH(BUILD) ON h.email = l.email
   WHERE l.type = 'landmark'
   AND h.type = 'hotel'
   limit 10;
3. Execute query. Or alternatively, click "Plan" or "Plan Text"

Actual:

Query attempts to run, but will likely be very slow and/or timeout because it's falling back to Nested Loop (and there may not be adequate indexing).

Expected/Suggested:

A warning icon shows in the Query Editor when attempting to use HASH join (see screenshot)

and/or

A warning icon shown in the Plan visualization that indicates that a Nested Loop Join is being used because HASH join is not supported in Community.