LG-6199: Show current IdV app step as page title

[aduth]

Why:

• As a user, I expect that each page is uniquely titled, so that I can understand its purpose.
• Feature parity with existing step implementation.

Testing Instructions:

1. Set idv_api_enabled: "true" in local config/application.yml
2. Go to: http://localhost:3000/verify/v2
3. Observe browser tab title is "Save your personal key - Login.gov"

Implementation Notes:

Based on current implementation:

identity-idp/app/views/layouts/base.html.erb

Lines 20 to 23 in e855581

	<%= content_tag(
	'title',
	content_for?(:title) ? raw("#{yield(:title)} - #{APP_NAME}") : APP_NAME,
	) %>

identity-idp/app/views/idv/personal_key/show.html.erb

Line 10 in e855581

<% title t('titles.idv.personal_key') %>

Screenshot:

[zachmargolis]

LGTM