Fix resource modelling inconsistencies across apps/instances/deployments (#49)

[DLondonoD]

What type of PR is this?

correction

What this PR does / why we need it:

Fixes five resource-modelling inconsistencies across apps/instances/deployments:

• Path naming: renames /appinstances to /app-instances, matching the
  hyphenated kebab-case naming used by every other multi-word path
  (/deployments, /clusters, /edge-cloud-zones).
• Single-resource GET: adds GET /app-instances/{appInstanceId}
  (getAppInstance) and GET /deployments/{appDeploymentId}
  (getAppDeployment), for consistency with /apps' getApp. The former
  list operations are renamed to getAppInstances/getAppDeployments to
  free up the singular operationId for the new by-id GETs.
• Location header consistency: fixes createAppInstance's 202
Location header, which described the URI as pointing at "the newly
  created application" (copy-paste from /apps) and had no working GET
  target — it now correctly describes the application instance and
  references the new getAppInstance endpoint. Adds an equivalent
  Location header to createAppDeployment's 202 response, aligning it
  with createAppInstance's pattern and pointing at the new
  getAppDeployment endpoint.
• Request/response schema split: splits AppManifest into a
  request-only shape (no appId, used by submitApp) and a new
  AppManifestInfo response shape (AppManifest allOf + required
  appId), used by both getApps' list items and getApp.
• getApp/getApps shape alignment: getApp's response is unwrapped
  to return AppManifestInfo bare, matching getApps' item shape instead
  of the previous { appManifest: AppManifest } wrapper.

Additionally, now that getAppInstance/getAppDeployment exist as
single-resource GET-by-id operations, removes the now-redundant
appInstanceId/appDeploymentId query filters from
getAppInstances/getAppDeployments respectively — filtering a list by
the exact id it's supposed to enumerate is redundant with calling the
by-id endpoint directly, and this also aligns both list operations with
getApps, which has no analogous id-in-query filter.

Test feature files were added/updated accordingly (getAppInstance.feature,
getAppDeployment.feature new; getAppInstances.feature,
getAppDeployments.feature, getApp.feature, getApps.feature,
createAppInstance.feature, deleteAppInstance.feature updated).

Which issue(s) this PR fixes:

Fixes #49

Special notes for reviewers:

This is a breaking change to path/operationId naming
(/appinstances → /app-instances, getAppInstance → getAppInstances,
getAppDeployments' query params), acceptable per the issue given the API
is still pre-1.0/rc. Reviewers should double check the AppManifest/
AppManifestInfo split doesn't affect any other operation still relying
on the original combined schema.

Changelog input

release-note Rename /appinstances to /app-instances;

Additional documentation

This section can be blank.

docs

[JoseMConde]

LGTM