fix(Config Schema): Recognize provider.websocketsDescription

[j0k3r]

I used it back with the v1 version, and now on v2 (at least) I got a Configuration warning when defining that value:

Serverless: Configuration warning at 'provider': unrecognized property 'websocketsDescription'

The value is used in different places but is missing in the config schema.
I've also updated the doc about it.

Simple schema to reproduce the warning:

service: serverless-ws-test

provider:
  name: aws
  runtime: nodejs12.x
  websocketsApiRouteSelectionExpression: $request.body.route
  websocketsDescription: Hi, I'm here to trigger a warning!

functions:
  wsHandler:
    handler: handler.wsHandler
    events:
      - websocket:
          route: $connect
      - websocket:
          route: $disconnect
      - websocket:
          route: $default

[codecov]

Codecov Report

Merging #10663 (31743bf) into main (e66c865) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main   #10663   +/-   ##
=======================================
  Coverage   86.40%   86.40%           
=======================================
  Files         299      299           
  Lines       12377    12379    +2     
=======================================
+ Hits        10694    10696    +2     
  Misses       1683     1683           

Impacted Files	Coverage Δ
lib/plugins/aws/provider.js	94.59% <ø> (ø)
bin/serverless.js	51.06% <0.00%> (+2.17%)	⬆️

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[pgrzesik]

Great catch, thanks a lot @j0k3r 🙇