Add configuration to skip copying assertion audience in JWT bearer grant type

[elatt]

Introduce a configuration option to control whether the audience from the assertion JWT is copied into the resulting access token in the JWT bearer grant type. By default, this behavior remains enabled. The implementation includes updates to the configuration interface, handler logic, and tests to ensure expected functionality.

[elatt]

I don't like how we need to have this be a pointer just to handle the default unset behavior. I'm thinking of just flipping the name of this param. However, I also wouldn't like inverting the logic of the flag because then you are dealing with a double negative 🤔

[elatt]

Suggested change

	// GrantTypeJWTBearerCopyAssertionAudience indicates whether the audience from the assertion JWT should be
	// copied into the resulting access token. Defaults to true for backwards compatibility.
	GrantTypeJWTBearerCopyAssertionAudience *bool
	// GrantTypeJWTBearerOmitAssertionAudience indicates whether the audience from the assertion JWT should be
	// copied into the resulting access token. Defaults to false for backwards compatibility.
	GrantTypeJWTBearerOmitAssertionAudience bool

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