Use GraphQl to store environment info

What does this MR do and why?

As part of allowing to select an agent in the Environment page, this MR updates the new_environment component to use GraphQl to update environment data. The change is behind the environment_settings_to_graphql feature flag.

Screenshots or screen recordings

No visual changes, the screenshot for the context:

How to set up and validate locally

1. Enable the environment_settings_to_graphql feature flag
2. Visit Project -> Build -> Environments page
3. Create an environment using the UI

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Review progress:

• backend developer review
• backend maintainer review
• frontend developer review
• frontend maintainer review

Related to #396407 (closed)