Problem

To start development of our new bill summary front-end features, we need to actually store the generated bill summaries somewhere.

Summary

This PR adds an optional summary field to our bill models that will contain the most recently generated LLM bill summary.

This is meant to give enough of an interface to unblock the front-end work - I expect there may be some additional summary storage to keep a historical archive of generated summaries as part of the actual summary backfill task, but I feel our most common query pattern is likely to just fetch the most recent summary whenever we fetch a bill, so I'd prefer to just keep a copy of that data on the bill itself anyway.

Checklist

[na] On the frontend, I've made my strings translate-able.
[na] If I've added shared components, I've added a storybook story.
[na] I've made pages responsive and look good on mobile.

Screenshots

N/A

Known issues

N/A

Steps to test/reproduce

Go to the Browse Bills and Bill Details page
See that it loads correctly

codeforboston / maple

Adding base summary field to bill models #1640