Feat/tie purchase flow

[ChiefStief]

Requirements List

• Ideally test against an API that requires the attestations be passed up to confirm that we are meeting criteria there. My sandbox is set up to do this or we can get Make 'attestations' field required when purchasing privileges #425 merged into whatever environment we need

Description List

• Refactored purchase flow to be in one page with subcomponents to support privilege purchase nav highlighting and most easily support total control of purchase flow and dynamic progress calculation
• Renamed purchase flow pages to be more easily found: PrivilegePurchase*
• Abstracted out purchase flow into PurchaseFlowState, PurchaseFlowStep and step level logic to better support step handling (find next step, clean state appropriately, redirect appropriately etc)
• Added AcceptedAttestationToSend model
• Made military affiliation attestation only show and send if user is military affiliated
• Added sending of attestations accepted to purchase API call and relevant serializer
• Improved test coverage
• Added ProgressBar Component
• Fixed safari display bug on SelectPrivileges screen

Testing List

• yarn test:unit:all should run without errors or warnings
• yarn serve should run without errors or warnings
• yarn build should run without errors or warnings
• Code review
• Try going through the privilege purchase flow process and confirm that the happy path works
• Now try navigating around the site, and with the back and cancel buttons and confirm that the form flow works as expected:

1. Back should always return to the previous flow step
2. Cancel should clear the flow entirely and bring the user to LicenseeDashboard screen
3. Navigating out of the flow while still in the app will retain the users progress (including privilege purchase successful), coming back to the flow should bring them back to the screen they left off at
4. Refreshing the page at any point or navigating with the url bar will clear the flow
5. Clicking finish on the Successful screen will clear the privilege flow and re-fetch the users updated privileges

Closes #302

Note: The behavior above is what I decided to implement to avoid complexity surrounding auto filling potentially changed form fields due to the server attestations being updated on the server, complexity surrounding form race conditions and caching user responses vs updated attestations.

I also opted not to use localStorage to have this data persist across sessions. What I did do was set up the form flow so that any of these alterations can be made more easily if it turns out they are desired.

[jsandoval81]

This is excellent 🚀 I really like the purchase-flow-state mechanism.

[jsandoval81]

@jlkravitz This is ready for your review.

[jlkravitz]

Looks good! Few questions/comments.

[ChiefStief]

@jlkravitz Ready for re-review.

[jlkravitz]

Looks great! @isabeleliassen Good to merge.