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 94.90%. Comparing base (f367a76) to head (1e9edb1).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #2748    +/-   ##
========================================
  Coverage   94.89%   94.90%            
========================================
  Files        1235     1236     +1     
  Lines       28254    28261     +7     
  Branches     6223     6415   +192     
========================================
+ Hits        26813    26820     +7     
+ Misses       1383     1370    -13     
- 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.

[bradenmacdonald]

I don't think dismissable should be a prop for the plugin slot. First of all, it's never false, and second of all, it should be up to the plugin contents to decide whether to show a dismiss button or not.

[bradenmacdonald]

I don't think this makes sense as a prop either. Just hard-code the default className on the div in the default contents, or move that wrapper div outside of the slot. This className won't necessarily apply to custom plugins that put different content in this slot.

[bradenmacdonald]

These two props don't seem to be used, so I think you can just use them on the default contents only; they don't have to be a plugin prop.

The plugin prop API needs to be stable so it's best to keep it as simple as possible and only include necessary properties.

[bradenmacdonald]

This word "Dismiss" won't be translated, so we need another way of specifying it.