feat: add example apps

[jsnwesson]

APER-3042

This PR includes:

• example apps that display the use of direct and iFrame plugins
• examples of using all four Plugin Operations (Insert, Modify, Wrap, Hide)
• a bug fix when using getConfig in usePluginSlot
• update how Plugin and PluginSlot retrieve intl using useIntl function from frontend platform

Steps to run example apps

Run npm install in the root directory, then

Using two terminals:

1. Run npm install inside both example app directories.
2. Run npm run start in both directories.

Alternatively, once the packages are installed in both apps, you can run the apps from the root directory.
1.npm run start runs the host MFE (example)
2. npm run start:plugins runs the child MFE (example-plugin-app)

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 94.57%. Comparing base (3d73607) to head (e70b31a).

Files	Patch %	Lines
src/plugins/data/hooks.js	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
+ Coverage   90.80%   94.57%   +3.77%     
==========================================
  Files          12       10       -2     
  Lines         174      166       -8     
  Branches       32       32              
==========================================
- Hits          158      157       -1     
+ Misses         14        7       -7     
  Partials        2        2              

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