lint: check blurb for exercises

[ee7]

This commit implements the below rules for the .meta/config.json file
of a Concept Exercise or a Practice Exercise.

• The "blurb" key is required
• The "blurb" value must be a non-empty, non-blank string with
  length <= 350

See:

• https://github.com/exercism/docs/pull/95/files
• https://github.com/exercism/docs/blob/f7d5ec6fda07/building/configlet/lint.md

---

This PR currently makes the below diff to the configlet lint output, per track.

ballerina

+Missing key: 'blurb':
+./exercises/practice/calculator-service/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/practice/echo-service/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/practice/greeting-service/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/practice/hello-world-service/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/practice/legacy-service-client/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/practice/order-management/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/practice/service-composition/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/practice/service-invocation/.meta/config.json
+

bash

+Missing key: 'blurb':
+./exercises/practice/list-ops/.meta/config.json
+
+Configlet detected at least one problem.
+For more information on resolving the problems, please see the documentation:
+https://github.com/exercism/docs/blob/main/building/configlet/lint.md

erlang

+Missing key: 'blurb':
+./exercises/practice/bracket-push/.meta/config.json
+

go

+Missing key: 'blurb':
+./exercises/concept/chessboard/.meta/config.json
+
+Missing key: 'blurb':
+./exercises/concept/the-farm/.meta/config.json
+
+Configlet detected at least one problem.
+For more information on resolving the problems, please see the documentation:
+https://github.com/exercism/docs/blob/main/building/configlet/lint.md

objective-c

+Missing key: 'blurb':
+./exercises/practice/bracket-push/.meta/config.json
+

php

+Missing key: 'blurb':
+./exercises/practice/ordinal-number/.meta/config.json
+
+Configlet detected at least one problem.
+For more information on resolving the problems, please see the documentation:
+https://github.com/exercism/docs/blob/main/building/configlet/lint.md

purescript

+Missing key: 'blurb':
+./exercises/practice/bracket-push/.meta/config.json
+

r

+Missing key: 'blurb':
+./exercises/practice/fizz-buzz/.meta/config.json
+

solidity

+Missing key: 'blurb':
+./exercises/practice/token-transfer/.meta/config.json
+

swift

+Missing key: 'blurb':
+./exercises/practice/bracket-push/.meta/config.json
+