Fix/deserialization of callback events

[Dovchik]

https://tickets.sinch.com/browse/DEVEXP-622
Adds Conversation.Webhooks.Deserialize.ParseEvent(string) method to deserialize hooks models.
For Conversation unit tests, use the same JsonSerializationOptions as inside ConversationClient to be sure of serialization consistency
Update Conversation.Webhooks.Update method to take first paramater as an Id of of a webhook

[asein-sinch]

The updates in this PR are going to the right direction, but in the current state, it's difficult to provide an approval:

• the referenced ticket is too vague about what needs to be done
• the PR is targeting the main branch which will trigger a new release upon merge. We have seen the difficulty to communicate about a version upgrade in the past, it would be better to cover all the deserialization cases in a single release
• to updated code is handling only a subset of messages types. Can you clarify the scope of this PR and confirm whether the other types of messages need to be updated or not?
  The E2E tests targeting the mocks from our official mockserver are passing because only a few types of messages are present. It would be better to add unit tests for this kind of code update.

[Dovchik]

Thanks for the review!

the referenced ticket is too vague about what needs to be done

Updated, it is more clear?

the PR is targeting the main branch which will trigger a new release upon merge. We have seen the difficulty to communicate about a version upgrade in the past, it would be better to cover all the deserialization cases in a single release
to updated code is handling only a subset of messages types. Can you clarify the scope of this PR and confirm whether the other types of messages need to be updated or not?
The E2E tests targeting the mocks from our official mockserver are passing because only a few types of messages are present. It would be better to add unit tests for this kind of code update.

Updated the description, it's more clear?
Regarding tests, do you expect to see specifically added Unit tests for models not present in E2E mocks?

[Dovchik]

Added unit tests for each webhook, fixing the models alongside. Json data is based on our Java SDK https://github.com/sinch/sinch-sdk-java/tree/main/openapi-contracts/src/test/resources/domains/conversation/v1/webhooks/events
Changed e2e conversation webhooks tests to use mock server data

Removed sms verification oas test. The idea is to get rid of all tests based on open api file as they are deemed flakey - the work is ongoing

[asein-sinch]

Please check pending comments that are still not answered. On my side:

• Fix/deserialization of callback events #92 (comment)
• Fix/deserialization of callback events #92 (comment)
• Fix/deserialization of callback events #92 (comment)
• Fix/deserialization of callback events #92 (comment)