feat: enable configurable header

[syedsajjadkazmii]

This PR makes the header configurable by accepting the custom menu in props. This replicates this feature from openedx/frontend-component-header. (Reference PR)

Details:
This PR adds the following functionality:

• Accept the main menu in the props. if not provided, the default main menu will be used.
• Accept the secondary menu in the props.
• Accept the user menu in the props.
• Restructure the user menu to add support for menu groups with heading in the user menu.
• This will not affect the current usages of the frontend-component-header-edx.

Screenshots of using custom headers for replicating different MFE headers.
Note: Screenshots are with local setup.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.66667% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 73.15%. Comparing base (2e76a03) to head (61a6c77).

Files	Patch %	Lines
src/Header.jsx	85.71%	2 Missing ⚠️
src/DesktopHeader.jsx	94.73%	1 Missing ⚠️
src/MobileHeader.jsx	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #560      +/-   ##
==========================================
+ Coverage   72.32%   73.15%   +0.82%     
==========================================
  Files          52       52              
  Lines         813      838      +25     
  Branches      158      171      +13     
==========================================
+ Hits          588      613      +25     
  Misses        215      215              
  Partials       10       10              

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[mubbsharanwar]

We should add/render a configurable Header in example/index.jsx as default components are added for local testing

[mubbsharanwar]

LGTM