Migrate Members modal to testid

What does this MR do and why?

As per gitlab-org/quality/quality-engineering/team-tasks#1822 (closed) , this migrates the QA E2E spec selector attributes used for Members Modal from data-qa-selector / :element_type to data-testid / 'element-type'

How to set up and validate locally

Run a test that uses members modal eg.

CHROME_HEADLESS=false bundle exec bin/qa Test::Instance::All http://gdk.test:3000/ ./qa/specs/features/browser_ui/9_data_stores/project/invite_group_to_project_spec.rb

Check the E2E pipeline / Allure report of this MR for passing / known unrelated issues.

MR acceptance checklist

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