Add onCancelCallback, onFailureCallback in LLM Chat View

[ONLYstcm]

• Added onCancelCallback to allow complete replacement of the default behavior of AdaptiveSnackBar when an LlmCancelException occurs.
• Added onFailureCallback to enable overriding the default behavior of AdaptiveAlertDialog for LlmFailureException and general LlmException.
• Added cancelMessage to allow CANCEL message to be changed when an LlmCancelException occurs.
• Added errorMessage to allow ERRORz message to be changed when an LlmCancelException` occurs.

Implements: #37

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[csells]

@ONLYstcm please include a new sample that shows off this capability.

[domesticmouse]

@ONLYstcm Please sign the CLA. We can't merge the PR without it

[ONLYstcm]

@csells @domesticmouse Please take a look now 🙏

CLA now signed

[domesticmouse]

PTAL @csells

[csells]

@ONLYstcm lgtm. only needs updates to the CHANGELOG.

[csells]

lgtm

[domesticmouse]

Sorry to do this, but can we look at adding some test coverage here?

The upside of having test coverage is that we won't break this functionality with future changes as this functionality will be checked by our friend the GitHub CI bot.

Thanks!

[domesticmouse]

Btw, update your PR to fix the beta CI issue. It was fixed in #51

[domesticmouse]

Landing as is