feat: add Page Banner Slot for Schedule and Details Page

[Anas12091101]

Description

This PR adds a Page Banner Slot in the Schedule and Details Page to allow customization of the banner message, which is currently hardcoded.

Useful information to include:

• Which user roles will this change impact? Course Author
• Include screenshots for changes to the UI (ideally, both "before" and "after" screenshots, if applicable).

By default:

Overridden by Slot:

Supporting information

https://github.com/mitodl/hq/issues/9362

Testing instructions

• Add the following settings to your edx-platform instance to display the banner on the Schedule and Details page:

MKTG_URLS = {
    "ROOT": "https://your-marketing-site-url"
}
FEATURES["ENABLE_MKTG_SITE"] = True

• Override the slot by following the readme added in this PR
• Verify the changes on the Schedule and Details page

Other information

Include anything else that will help reviewers and consumers understand the change.

• Does this change depend on other changes elsewhere?
• Any special concerns or limitations? For example: deprecations, migrations, security, or accessibility.

Best Practices Checklist

We're trying to move away from some deprecated patterns in this codebase. Please
check if your PR meets these recommendations before asking for a review:

• Any new files are using TypeScript (.ts, .tsx).
• Avoid propTypes and defaultProps in any new or modified code.
• Tests should use the helpers in src/testUtils.tsx (specifically initializeMocks)
• Do not add new fields to the Redux state/store. Use React Context to share state among multiple components.
• Use React Query to load data from REST APIs. See any apiHooks.ts in this repo for examples.
• All new i18n messages in messages.ts files have a description for translators to use.
• Avoid using ../ in import paths. To import from parent folders, use @src, e.g. import { initializeMocks } from '@src/testUtils'; instead of from '../../../../testUtils'

[openedx-webhooks]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.95%. Comparing base (f367a76) to head (735751e).
⚠️ Report is 39 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2748      +/-   ##
==========================================
+ Coverage   94.89%   94.95%   +0.05%     
==========================================
  Files        1235     1246      +11     
  Lines       28254    28642     +388     
  Branches     6223     6528     +305     
==========================================
+ Hits        26813    27198     +385     
+ Misses       1383     1373      -10     
- Partials       58       71      +13     

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[bradenmacdonald]

Thanks for the nice PR. I have a few concerns about the plugin slot props, and hope we can simplify them. Otherwise this looks great.

[Anas12091101]

@bradenmacdonald, sorry for the delay; I was on vacation. This is ready for another look

[bradenmacdonald]

No problem @Anas12091101 , so was I. This looks great now. Thanks for making those changes.