fix: make sidebar (and content) fill the whole page

[rpenido]

Description

This PR increases the sidebar height to fill the entire page.

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

Before

After

Supporting information

Related to: #2523 (comment)

Testing instructions

• Open a library's import page, accessing Tools > Import inside a library.
• Check the sidebar height

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]

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 94.95%. Comparing base (0f20267) to head (cb5d6d0).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2777      +/-   ##
==========================================
- Coverage   94.95%   94.95%   -0.01%     
==========================================
  Files        1245     1245              
  Lines       28639    28637       -2     
  Branches     6508     6511       +3     
==========================================
- Hits        27195    27193       -2     
  Misses       1373     1373              
  Partials       71       71              

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[ChrisChV]

Looks good 👍

• I tested this: I followed the testing instructions
• I read through the code and considered the security, stability and performance implications of the changes.
• I tested that the UI can be used with a keyboard only (tab order, keyboard controls).