Support change in audit threshold

[jadudm]

Squad: TBD Timeframe: Must apply to submissions whose audit year begins October 1, 2024 and after.

The threshold for Single Audit submissions is changing from $750K to $1M.

What problems are we trying to solve?

This is the policy in the new UG.

An entity with a Fiscal Year starting on or after October 1, 2024 must submit at a $1M threshold.

An entity with a Fiscal Year starting before October 1, 2024 must submit at the $750K threshold.

What we can do today

We will need to address several things.

Audit creation

We need to rethink how the introduction to audit creation takes place. This will provide an opportunity to address several known weaknesses in the opening sequence:

1. Users cannot currently revisit any of these questions. This has been a pain point for users. It should be possible to revisit all of these questions from the checklist.
2. We can turn this multi-step form into a single form (if we want), simplifying implementation.
3. We can ask different questions about the threshold.

Validations

We will need to improve our validations around this space. We recently added Federal Award checks that will need to be updated; we will want to check the reported FY start date and total amount expended, and make sure that they are reporting correctly. (E.g. a date before Oct 1, 2024 must clear $750K in expenditures, etc.).

Context and further reading

Any number of auditing houses have provided summaries, and there is the UG itself.

### Tasks
- [x] Update documentation (fac.gov) to align with guidance, making clear timelines and thresholds
- [ ] Update submission templates where appropriate
- [ ] Update app.fac.gov copy
- [ ] Update app.fac.gov audit creation sequence
- [ ] Update app.fac.gov validations to correctly apply thresholds
- [x] Update all help desk materials (FAQ + macros) where thresholds are mentioned

[James-Paul-Mason]

Just documenting here that some FAQs and macros will need attention in addition to the static site.

[jadudm]

@James-Paul-Mason , it might be worth either 1) expanding the ticket or 2) ticketing the work separately, and linking back to this ticket. That way, the reminder that it needs to happen is explicitly tracked. Even if they're thin tickets to start, they'll enter the Triage column, and we won't lose site of them.

[James-Paul-Mason]

Content work has already been ticketed separately in #4198. I'll be working from that ticket, but I will also come back to this ticket to check off the relevant content tasks from the list when complete.