Refactor msgid, parameterize msgstr with agency-specific content

[thekaveman]

A number of the msgstr in the current PO files are partially generic, but also partially reference a specific agency or agency's programs. For example, the success message after eligibility is verified via Login.gov:

msgid "enrollment.pages.index.mst_login.eligibility_confirmed_item.details"
msgstr ""
"Your eligibility has been verified by Login.gov. This benefit will give you "
"a half-price fare on public transportation with MST."

We want to be able to reuse the first part of this message across many agencies, and also to parameterize the second part to swap in the specific agency (and their discount if applicable).

Acceptance Criteria

• Every msgstr that references a specific agency (or a specific agency's programs) directly, is either parameterized to accept the agency details or broken out into a minimal msgid/msgstr block
• Every msgid corresponding to the above parameterized msgstrs is free from any specific agency identifier

Additional context

Corollary to #1186