[BugFix] Handle configs which have missing options for MsSql

[Aniruddh25]

Why make this change?

• With the recent refactor Overhaul of config system #1402, if options property is not specified in the config, after deserialization the Options dictionary of DataSource object is null
• This leads to a null dereference when trying to GetTypedOptions(MsSqlOptions) here.

What is this change?

• Make Options a nullable property since its not required as per the schema.
• Handle all the instances of Options considering it could be null.

How was this tested?

• Manually running dab.
• Automated tests:
  1. Removed the options: set-session-context from the initial config used in the CLI tests to verify deserialization results in a null Options dictionary as demonstrated by the Snapshots
  2. Modified tests which create a custom config and start the engine by setting Options to null and verifying those continue to pass.
  Note: The checked in configuration file for MsSql sets the session context to true for integration tests of row level security feature. So, did not modify that file even though options is optional for MsSql.

[seantleonard]

Thanks for adding. Pending addressing ci/cd build error

[ayush3797]

LGTM!