Adds CardClicked to enum MessageType so that backends sending CardClicked events can leverage it on their custom backends.

Description

Adds CardClicked to enum MessageType so that backends sending CardClicked events can leverage it on their custom backends.

Related Issue

Add CardClicked to enum MessageType #98

Motivation and Context

Custom backends like Google Chat also send CardClicked events for interactive cards when buttons or images are clicked. This will allow the additional MessageType so that backends can leverage it natively

How Has This Been Tested?

Tested with PoshBot.GChat.Backend in local.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes. N/A for this, tests don't exist (yet) for enums
• All new and existing tests passed.