Validate and update Specs for correctness

[AlexandraRoatis]

Problem
The documented specification does not reflect the current state of the implementation (v1 API).
This issue will be used to track different aspects of the spec update.

Persona:
Which persona is this feature for?

• System Integrator
• Contributor

Exit Criteria
Solve the following set of issues:

• update spec.md (issue Update object model spec with v1 api #4092)
• update interfaces.md
• update data-plane.md
• update channel.md
• update sources.md
• add specifications for Sequence and Parallel
• move the produced events details from spec.md to spec-adjacent documentation (issue Move the produced events details out of spec.md #4596)

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[lberk]

@AlexandraRoatis is this issue still relevant? (v0.20 was released several weeks ago)