Feat: manual variable tab in pipeline detail

What does this MR do and why?

• Frontend part of #323097

• Add route for manual variables.
• Add bootstrapper script for manual variable tab.
• Add more data to pipeline helper for manual variable tab.
• Add frontend table component for displaying variables.
• Add frontend empty component for displaying empty state.
• Add new graphql for fetching manual variables.

/cc @luzhiyuan.deer

Changelog: added

MR acceptance checklist

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

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

State	Screenshot
Empty
Maintainer Role with data concealed (15+ data)
Maintainer Role with data revealed (15+ data)
Maintainer Role with data concealed (< 15 data)
Developer Role (15+ data)

How to set up and validate locally

1. Checkout to this commit.
2. Go to any projects with pipeline configured (with maintainer role).
3. Create a manual pipeline with manual variables.
4. Go to the triggered pipeline detail page and click on the Manual Variables tab
5. Observe.

• Switch account to a developer role repeat step 2-5.