Adds protoc-gen-connect-openapi as plugin for apiv2

[raphaelvrosa]

Description

Replaces kollalabs with protoc-gen-connect-openapi plugin for apiv2 auto-generation of OpenAPI spec in apiv2.
The new plugin is more flexible and generates proper/extensive validation rules, besides it generates proper enum messages.
In addition, this PR adds:

• Proper error parsing and return in REST API, filtering the error details in the returned message;
• Adds missing fields from previous api (e.g., instance_status_detail)
• Defines page_size and offset as uint32 (integer in openapi spec)
• Sets maximum values for start/end seconds in single schedule

Fixes # (issue)

Any Newly Introduced Dependencies

Please describe any newly introduced 3rd party dependencies in this change. List their name, license information and how they are used in the project.

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Checklist:

• I agree to use the APACHE-2.0 license for my code changes
• I have not introduced any 3rd party dependency changes
• I have performed a self-review of my code

[pierventre]

please inform app-orch team of this change