feat: agentic chat availability

Description

The MR introduces control over the appearance of the Duo Agentic Chat in VSCode.

Description	Result
No git project opened, no Agentic Chat
Opened project isn't from the connected instance, no Agentic Chat
Opened project is from the connected instance, but "Experiment and beta features" is disabled on the group level, or the instance license is lower than Premium. No Agentic Chat
Opened project comes from Premium/Ultimate license and group has "Experiment and beta features" enabled. Agentic Chat available

Why not in the LS state?

This MR is a quick win considering the time constraints for delivering this features. We will move this login into the LS state as the next step.

How has this been tested?

• If src/browser or src/common has been modified, please consider interoperability with the Web IDE. See Running the Extension in WebIDE.
• Consider an end-to-end test for significant new features that aren't covered by integration tests.

Screenshots (if appropriate)

What CHANGELOG entry will this MR create?

• fix: Bug fix fixes - a user-facing issue in production - included in changelog
• feature: New feature - a user-facing change which adds functionality - included in changelog
• BREAKING CHANGE: (fix or feature that would cause existing functionality to change) - should bump major version, mentioned in the changelog
• None - other non-user-facing changes

References https://gitlab.com/gitlab-org/gitlab/-/issues/540750