Trigger shared runner credit card validation alert on click, make it always dismissable

What does this MR do and why?

For #339949 (closed)

This MR changes the flow of the alert that blocks a user from enabling shared runners for a project if they haven't done credit card validation: it makes the toggle visible from the start, then shows the same dismissable alert each time enabling the toggle fails for that reason.

This change is behind the <code data-sourcepos="7:29-7:63">ci_require_credit_card_on_free_plan</code> feature flag, so it doesn't require changelog/documentation.

Screenshots or screen recordings

scenario	before	with this MR
try to enable shared runners without credit card validation	toggle is initially hidden by dismissable alert, then clicking the toggle triggers a non-dismissable alert Screen_Recording_2022-01-31_at_14.13.32	toggle is initially shown, same dismissable alert is triggered each time toggle is clicked Screen_Recording_2022-01-31_at_12.47.03

How to set up and validate locally

1. git checkout 339949-action-based-dismissable-credit-card-validation-alert
2. echo "Feature.enable(:ci_require_credit_card_on_free_plan)" | rails c
3. in ee/app/models/ee/user.rb, make requires_credit_card? return true for testing purposes:

    def requires_credit_card?(project)
      true
    end

4. navigate to Settings => CI/CD for a project and expand the Runners section
5. click the Enable shared runners for this project toggle - the alert should appear
6. dismiss the alert and try again - the same alert should appear each time

MR acceptance checklist

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