Medicare cardholder: configure flow in `test` for CST

[thekaveman]

Related to #2356

Acceptance criteria

• [x] A new EnrollmentFlow instance is created via the test Admin
• [x] The new flow's system name is medicare
• [x] The new flow is configured with appropriate IdG connection, and scope and claim #2364
• [x] The new flow is configured with templates created by related issues
  • [x] #2350
  • [x] ~#2351~ used in the radio button template, doesn't need to be configured on the model
  • [x] #2352
  • [x] #2358
  • [x] #2414
• [x] The new flow is configured with a label, the copy of which matches the label from selection_label_template
• [x] The new flow is configured with a group ID for the group created for #2356
• [x] The new flow is added to the CST transit agency
• [x] The new flow is first in the list of all CST flows (show it shows up first on the eligibility:index page)
• [x] The new flow confirms eligibility using a valid sample Medicare.gov account

[angela-tran]

Done!