[SG-35191] Accessibility: Announce updates on inputs that control live page state

Created by: gitstart-sourcegraph

Description

1. Typing in this pattern input filters the number of results that are matched. It's difficult to determine if the user's input is actually filtering correctly or if there's a typo that matches nothing without navigating the page a significant amount.
2. This is also true on the site-admin repo filters available on code intelligence policy edit pages.

Refs

SourceGraph Issue GitStart Issue

Expected behavior

These should be announced as the user types, or at the very least we should have an auxiliary count attached to the form input as a hint or label.

Test plan

1. Toggle the disabled prop to false on the ObjectMatchingGitPattern.tsx.
2. Navigate to the configuration here.
3. Use the screen reader and type in the pattern input and hear it announce your result.

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.