Categorizing Conflict error codes

[ayush3797]

Why make this change?

To recognize exceptional conditions like insertion of rows with duplicate key as Conflicting operations (return exception with HttpStatusCode 409), rather than throwing InternalServerError. This is just one example, and we can have other conflicting operations in the database as well.

What is this change?

Added a set ConflictExceptionCodes to DbExceptionParser.cs which will store the error numbers to be considered for returning exception with HttpStatusCode 409.

How was this tested?

Added regression test to InsertApiTestBase.cs class (overridden in each of the child class), which tries to insert a row with duplicate primary key into the database table and thus fails accordingly throwing exception with 409 status code.

Additional Change:

Till this point, the test result verification expected the actual and expected exception messages to be exactly the same. However, the test added in this PR InsertOneTestViolatingUniqueKeyConstraint returned a dynamic exception message changing on every test run for MsSql. For such dynamic cases, we can now have an option isExpectedErrorMsgSubstr which if set to true, will only look for a substring (which remains constant among multiple test runs) in the actual error message, rather than expecting them to be identical.

Sample Request(s)

1. REST Endpoint: https://localhost:5001/api/commodities/
   Database chosen: MsSql
   Request: {
   "categoryName": "SciFi",
   "pieceid":"1",
   "categoryid": "1"
   }
   Response: {
   "error": {
   "code": "DatabaseOperationFailed",
   "message": "Violation of PRIMARY KEY constraint 'PK__stocks__9CC9595F28BE875B'. Cannot insert duplicate key in object 'dbo.stocks'. The duplicate key value is (1, 1).",
   "status": 409
   }
   }

[seantleonard]

some nits/ suggestions

[aaronburtle]

Overall looks good, just a question, plus a request to use system.text.json if possible

[Aniruddh25]

LGTM, thanks for the change!