feat: add deprecation warning to create legacy library form [FC-0123]

[rpenido]

Description

Adds the following warning banner to the Create Legacy Library page:

Useful information to include:

• Which user roles will this change impact?
  "Course Author"

Supporting information

• Related to [verawood] Legacy Libraries DEPR: Warnings in the UI #2876

Testing instructions

• Open the Create Legacy library form (Legacy Libraries > + New Library) and check the warning

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'

---

Private ref: FAL-4333

[openedx-webhooks]

Thanks for the pull request, @rpenido!

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.56%. Comparing base (d0d593e) to head (128e5c4).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #2963    +/-   ##
========================================
  Coverage   95.56%   95.56%            
========================================
  Files        1350     1350            
  Lines       31128    31129     +1     
  Branches     6817     7052   +235     
========================================
+ Hits        29747    29748     +1     
  Misses       1331     1331            
  Partials       50       50            

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[navinkarkera]

@rpenido Looks good.

[ChrisChV]

Looks good!