EAM API: singular zone declarative app instance post API

[gainsley]

What type of PR is this?

• correction
• enhancement/feature

What this PR does / why we need it:

• Deploy an AppInstance to a single Zone instead of multiple zones. This avoids confusion about the behavior if one or more of the multiple zone deployments fails, see EAM: Suggest that POST appinstance targets a single EdgeCloudZone #256.
• Assign a name to the AppInstance. Without this we cannot have declarative/infrastructure-as-code clients layered on top of the NBI API. See EAM: Suggest to add App Instance Name #255. Also makes it consistent with other objects that also have names, i.e. Apps, EdgeCloudZones.
• Adds more necessary information to the returned AppInstanceInfo, including the AppId (previously no way to figure out which App the AppInstance was an instance of). Makes the necessary information required. Changed the EdgeCloudZoneName to an EdgeCloudZoneId for consistency, as we always reference other objects by their ID, not their name.

Which issue(s) this PR fixes:

Fixes #256, #255

Special notes for reviewers:

Changelog input

 release-note
- appinstance post API targets a single zone instead of multiple zones and requires a name for declarative and infrastructure-as-code clients, added more information to appinstanceinfo

Additional documentation

docs