Address r1.1 review findings in the API definition and test definitions

[maheshc01]

What type of PR is this?

• correction
• cleanup
• tests

What this PR does / why we need it:

Prepares the API definition and test definitions for the r1.2 release candidate by resolving the content-related review findings collected in #37 from the r1.1 alpha review:

• Reuses the Rate / RateUnitEnum schemas from QualityOnDemand for the response and renames the property to maxDownstreamMediaRate.
• Clarifies that the returned value is the maximum downstream media streaming rate the network allows for the device, as enforced for media traffic, not a measurement or forecast of the throughput the device will actually experience.
• Corrects externalDocs.url to point to this repository.
• Declares error responses explicitly with only the codes this API can return. 500 is removed; 429 is kept (see Check whether 429 and 500 errors are needed for this API #40).
• Consolidates the test definitions into a single media-streaming-rate.feature covering happy path, request validation, the Commonalities C01 device error scenarios, 401 and 403.
• Updates the README scope section.

The spec validates cleanly against the CAMARA Spectral r4 ruleset and the feature file against the CAMARA gplint configuration.

Which issue(s) this PR fixes:

Fixes #39
Fixes #41
Fixes #42

Partially addresses #40 (500 removed; 429 will be finalised with the Commonalities r4.4 alignment). Part of #37.

Special notes for reviewers:

• The API rename to device-media-streaming-rate (Repository name does not match API name #38) is deliberately not in this PR. It is in Rename API to device-media-streaming-rate #49, stacked on this branch, so that this PR validates green. The validation rules tie the file name to release-plan.yaml and forbid changing the release plan alongside other files, so the rename and the release-plan update (Release plan: r1.2 release candidate on Commonalities r4.4 #48) cannot both be green while the other is unmerged. Intended order: this PR, then Rename API to device-media-streaming-rate #49, then Release plan: r1.2 release candidate on Commonalities r4.4 #48.
• The switch to the Commonalities r4.4 error response catalogue follows in a further PR once the code/common sync for r4.4 has landed.
• Property rename maxDownstreamMediaBitRateSupported + unit to maxDownstreamMediaRate (Rate object) is a breaking change relative to 0.1.0-alpha.1, which is acceptable for a 0.x API moving to rc.

Changelog input

 release-note
- Breaking: response property maxDownstreamMediaBitRateSupported + unit replaced by maxDownstreamMediaRate (Rate object with value and unit)
- Changed: description clarifies the returned value is the maximum rate the network allows for the device, not a throughput measurement or forecast
- Changed: error responses declared explicitly with only applicable codes; 500 INTERNAL no longer documented
- Fixed: externalDocs.url points to this repository
- Added: consolidated test definitions in media-streaming-rate.feature

Additional documentation

docs

[camara-validation]

CAMARA Validation — PASS

0 errors, 0 warnings, 0 hints | Profile: standard

View full results

[maheshc01]

@Kevsy Please review these changes based on the review comments you had shared. I will create a separate PR for yaml and api name changes as its causing failures in automated validations.