[MRF-5] PLU-520: refactor frontend to allow test step on mrf actions

[pregnantboy]

Changes

• MRF steps should use FormSGCheckAgainButton
• onSaveAndTestStep should not try to save step if it's a hidden action

Refactors

• Refactored addStaticSubsteps to only add testStep substep if there's no fields to modify
• Added cache-first fetch policy to the ChooseConnectionSubstep to improve performance
• Small refactor of Save + Check step buttons
• Added isMrfStep flag to the step metadata to properly handle FormSG MRF submissions

How to test?

1. Check step/Save button should render properly for all existing actions
2. Check step should render for MRF actions
3. Should be able to click Check step for MRF actions although not implemented yet

[pregnantboy]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• [MRF-8] PLU-520: New Approve-Reject component (frontend) #1284 : 2 dependent PRs (#1285 , #1349 )
• [MRF-7] PLU-520: remove mrf actions steps if necessary #1275
• [MRF-6] PLU-520: testStep for mrf actions should test multiple steps #1269
• [MRF-5] PLU-520: refactor frontend to allow test step on mrf actions #1268 👈 (View in Graphite)
• [MRF-4] PLU-520: automatically create/delete/update mrf steps on check step #1267
• [MRF-3] PLU-520: introduce mrf action that cannot be added by user #1266
• [MRF-2] PLU-520: parse formsg workflow data + refactor #1265
• [MRF-1] PLU-520: allow mrf forms to be connected #1264
• mrf/trunk

This stack of pull requests is managed by Graphite. Learn more about stacking.

[datadog-opengovsg]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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[linear]

PLU-520 MRF: Approvals

[kevinkim-ogp]

lgtm!
only have a small nit