Add Support for apps.manifest.* Endpoints

[misscoded]

Add support for the following apps.manifest.* methods:

apps.manifest.create apps.manifest.validate apps.manifest.update apps.manifest.delete apps.manifest.export

Category (place an x in each of the [ ])

• [ ] bolt (Bolt for Java)
• [ ] bolt-{sub modules} (Bolt for Java - optional modules)
• [x] slack-api-client (Slack API Clients)
• [ ] slack-api-model (Slack API Data Models)
• [ ] *slack-api--kotlin-extension** (Kotlin Extensions for Slack API Clients)
• [ ] slack-app-backend (The primitive layer of Bolt for Java)

Requirements

Please make sure if this topic is specific to this SDK. For general questions/issues about Slack API platform or its server-side, could you submit questions at https://my.slack.com/help/requests/new instead. :bow:

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to the those rules.

[cts5ws]

Is this still being prioritized?

[seratch]

@cts5ws Yes! but we're planning to add the support when those APIs are GAed.