Expose is_enterprise_install field

[7ail]

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Should this be an issue instead

• is it a convenience method? (no new functionality, streamlines some use case)
• exposes a previously private type, const, method, etc.
• is it application specific (caching, retry logic, rate limiting, etc)
• is it performance related.

Just exposing an existing field within the InteractionCallback object returned from Slack.

[7ail]

@parsley42 👋🏻 Hey, can I get this reviewed and merged please. Thanks.

[parsley42]

Trivial