Eliminate code duplication requests between Upsert and Insert

[aaronburtle]

Why make this change?

Closes #3209

What is this change?

Allow Upserts coming from REST requests to fall through to the Insert logic when auto-generated primary keys are missing. This eliminates code duplication between these two ops in the SqlMutationEngine

Add a test to cover the case when we have a PUT/PATCH with keys provided in the request body.

How was this tested?

New test was added to ensure complete coverage over the scenarios introduced with the keyless PUT/PATCH change.

Sample Request(s)

PUT that updates existing row (expects 200 OK):

PUT https://localhost:5001/api/magazine
Content-Type: application/json

{
    "id": 1,
    "title": "Updated Vogue",
    "issue_number": 9999
}

PUT that inserts new row (expects 201 Created):

PUT https://localhost:5001/api/magazine
Content-Type: application/json

{
    "id": 5001,
    "title": "Brand New Magazine",
    "issue_number": 42
}

PATCH that updates existing row (expects 200 OK):

PATCH https://localhost:5001/api/magazine
Content-Type: application/json

{
    "id": 1,
    "title": "Updated Vogue"
}

PATCH that inserts new row (expects 201 Created):

PATCH https://localhost:5001/api/magazine
Content-Type: application/json

{
    "id": 5001,
    "title": "Brand New Magazine"
}

[aaronburtle]

/azp run

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