Add Support for apps.manifest.* Endpoints

[misscoded]

Description

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

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

What type of issue is this? (place an x in one of the [ ])

• [ ] bug
• [x] enhancement (feature request)
• [ ] question
• [ ] documentation related
• [ ] testing related
• [ ] discussion

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

• [x] I've read and understood the Contributing guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [x] I've searched for any related issues and avoided creating a duplicate issue.

[filmaj]

Bumping this to 6.7, and FYI support for this exists on the feat-app-manifests branch.

[wcauchois]

Any update on support for these endpoints? 🙏