fix: align event subscription/notification to Commonalities r3.2

[mohdfarhanakram]

What type of PR is this?

correction

What this PR does / why we need it:

Aligns the Session Insights API event subscription and notification model to the CAMARA Commonalities r3.2 Event Subscription and Notification Guide.

• Aligned sink definition with URI format, HTTPS pattern validation, and example
• Replaced plain string sinkCredential with proper SinkCredential object schema (with AccessTokenCredential, PlainCredential, RefreshTokenCredential subtypes)
• Added 400 INVALID_SINK error response (along with INVALID_CREDENTIAL, INVALID_TOKEN, INVALID_ARGUMENT) with examples
• Renamed subscription-ends → subscription-ended with terminationReason enum (NETWORK_TERMINATED, SUBSCRIPTION_EXPIRED, MAX_EVENTS_REACHED, ACCESS_TOKEN_EXPIRED, SUBSCRIPTION_DELETED)
• Added subscription-started lifecycle event with initiationReason
• Added subscription-updated lifecycle event with updateReason
• Renamed EventType → SubscriptionEventType with description
• Fixed types / subscribedEventTypes property name mismatch in SessionRequest (required field referenced non-existent property)
• Added SubscriptionStatus enum (ACTIVATION_REQUESTED, ACTIVE, INACTIVE, EXPIRED, DELETED)
• Renamed startTime → startsAt per r3.2 convention
• Removed sinkCredential from response schemas (must not be returned per security guidelines)

Which issue(s) this PR fixes:

Fixes #70

Special notes for reviewers:

• Credential schemas (SinkCredential, AccessTokenCredential, etc.) follow the exact same pattern used in QualityOnDemand
• MQTT protocol support is kept as-is but sink credential now uses the proper object schema for both HTTP and MQTT
• The subscribedEventTypes → types fix also corrects a bug where SessionRequest.required referenced a non-existent property name

Changelog input

Aligned event subscription/notification model to Commonalities r3.2. Added SinkCredential schemas, subscription lifecycle events, SubscriptionEventType enum, SubscriptionStatus, and INVALID_SINK error response.

Additional documentation

• CAMARA Event Subscription and Notification Guide (r3.2)

[Kevsy]

LGTM 👍

[benhepworth]

Thanks for the PR @mohdfarhanakram - great progress aligning with Commonalities r3.2. Most everything is pretty solid - just a few recommendations that I added in-line. Summary of these recommendations:

• suggest renaming BadRequest400 to CreateSessionBadRequest400 and then creating a new Generic400 for the other calls since the sink specific errors only apply when creating a session (see model QoD uses for reference)
• question about uri for http/mqtt - http is a URI but not technically for mqtt, which is why the original was a string - needs more discussion with the group, will address on the next call.
• made status required in SessionBase since there should always be a current state of the subscription (equivalent of QoD qosStatus, which is required in it's SessionInfo).

[benhepworth]

we should discuss this more - the reason it was originally a string is because a MQTT topic is not technically a URI by definition.

[benhepworth]

will look up in Commonalities to align with that

[benhepworth]

we should leave this as a string for the generic SessionBase.sink since both HTTP and MQTT share it -- and add format:uri to HTTPSessionRequest.sink

[mohdfarhanakram]

Updated - removed format: URI from SessionBase.sink so it stays as a plain string (since MQTT topics aren't URIs). HTTPSessionRequest.sink retains format: URI as expected.