Veterans: add Sign Out link for Veterans/Login.gov flow

[machikoyasuda]

closes #1707

What this PR does

• Rename the button--sign-out--senior and link--sign-out--senior files to use --login-gov suffix
• Add sign_out_button_template, sign_out_link_template to Veteran's

How to test this PR

For the Veterans flow and the Senior flow:

• Display Sign out of Login button on Enrollment view
• Display Sign out of Login button on Eligibility Error view This one is hard to test)
• Display Sign out of Login button on Payment Error view (This one is hard to test)
• Display Sign out of Login button on Enrollment Success view

How I tested this locally

• Since the Login.gov/VA IDG flow is not yet available, I faked it by setting my VA Auth Provider to have the same exact configuration as the Senior one, and went thru the flow to at least confirm that the sign out link and buttons are showing up:

[machikoyasuda]

Ready for review @thekaveman @angela-tran

[thekaveman]

@machikoyasuda @angela-tran

Since the Login.gov/VA IDG flow is not yet available

It is now available and should work from localhost:11369 and dev-benefits, see this long thread in Slack for configuration details: https://cal-itp.slack.com/archives/C037Y3UE71P/p1694210616556309

I updated the Benefits Test Data doc with info about how to create a sandbox Login.gov user that verifies as a Veteran.

[thekaveman]

@machikoyasuda want to rebase this on the changes from those other PRs?

[machikoyasuda]

Tested locally: Veterans log out

[thekaveman]

Looks good. I see the link and was able to sign out from:

✅ Eligibility Fail
✅ Enrollment Start
✅ Enrollment Success