feat(isValidGraphQLQuery): add validation for graphQl queries and test

[abhay-bharat]

isValidGraphQLQuery validator has been added to the bucket of existing validators, it is in the file src/lib/isValidGraphQLQuery.js and added tests to /test/validators.test.js.

It parses the query string using the parse function from graphql package library. Reference Parser

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)
• References provided in PR (where applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (72573b3) to head (82aa392).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2569   +/-   ##
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  Coverage   100.00%   100.00%           
=========================================
  Files          114       115    +1     
  Lines         2535      2554   +19     
  Branches       641       646    +5     
=========================================
+ Hits          2535      2554   +19     

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