Update the icon in the manual variable button

What does this MR do and why?

Resolves #387308 (closed)

• Updates delete button in manual variable form from an x to a trash can.
• Updates the tooltip label
• Updates the margin

See issue for designs

Screenshots or screen recordings

before	after

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

• Make sure you have runners setup in GDK: https://docs.gitlab.com/runner/configuration/macos_setup.html
• Navigate to CI/CD > Editor
• Set up a manual job in your editor. Assuming your have 2 variables, varOne and varTwo, you can use this:

manual_job:
  script:
    - echo "$varOne" "$varTwo"
  when: manual
  rules:
    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

• Navigate to the manual job after committing your change, which should automatically run a pipeline. (CI/CD > Jobs)
• Add some variables and note the delete icon on the right side of the row

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.