Add the ability to add a group's o11y service settings

What does this MR do and why?

Add the ability to create an 011y service setting for a group by ID.

References

• Add the ability to create new o11y service records for a group

Screenshots or screen recordings

Screen_Recording_2025-08-22_at_12.23.02_PM

How to set up and validate locally

1. In rails console enable the experimental_access FF, and note how many setting records you have

Feature.enable(:experimental_access, User.first)
Observability::GroupO11ySetting.count

2. Navigate to http://localhost:3000/-/experimental/o11y_service_settings/new and fill out the form.
3. Verify the count of settings increased:

Observability::GroupO11ySetting.count

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.