add separate fetchers for rollback and commit message data

[TimothyMothra]

Fix issue #782 .

Short description of the fix:
SqlClient is including a TransactionName property in transaction rollback messages (but not in transaction commit messages). Added a separate “fetchers” for the rollback message data.

• I ran all unit tests locally
• CHANGELOG.md updated

[anpete]

I think you need to handle the transaction After and Error cases, too. Add TransactionName to the message in this unit test: https://github.com/Microsoft/ApplicationInsights-dotnet-server/blob/develop/Src/DependencyCollector/Shared.Tests/Implementation/SqlClientDiagnosticSourceListenerTests.cs#L508

[anpete]

Consider adding a unit test for the Rollback error case.

[Dmitry-Matveev]

@anpete, I looked and After and Error fetchers, they seem to only care about the subset of the available fields anyway - do you expect them to fail as well if there no 1:1 match? @MS-TimothyMothra can expand this PR to modify fetchers for those as well and add them into the separate blocks within switch if required - I would just like to confirm with you if it is.

[anpete]

@Dmitry-Matveev IIRC the key thing is that a fetcher may never be used with more than one incoming message type (anonymous object shape). We need to have unit test coverage for all of the events we handle, and in those tests we should be careful to construct exact replicas of the actual SQL Client message payloads.

[TimothyMothra]

I'm marking this PR as resolved and will confirm that we have unit tests for every possible type in a follow up issue: #796