feat: import feature (experimental)

[kptdobe]

Do not merge until validated with 5 customers (dev users)

This adds a default import capability: on non-helix site, run a predefined import with basic capabilities (see adobe/helix-importer#261) and visualise the result in a popup window. Result is very similar to the View Document Source feature but... for a non-helix website!

To test:

• open any non-helix site
• click on the Sidekick button
• hit the View imported document button 

This depends on:

• feat: major redesign - get rid of JSDOM helix-importer#260
• feat: improve default import helix-importer#261

Before merging, the PR still needs some minor adjustments:

• finalise the button / feature name
• translations ?
• remove the Experimental Sidekick name!

A version of the Sidekick with the feature enabled can be downloaded here: https://adobe-my.sharepoint.com/:u:/r/personal/acapt_adobe_com/Documents/helix/shared/AEM%20Sidekick%20-%20(View%20imported%20document)%20experimental.zip?csf=1&web=1&e=YB32gf
To install it:

• download the zip
• unzip it locally
• go to chrome://extensions/
• enable Developer Mode (top right corner)
• Load Unpacked - select the unzipped folder
• you can have both extensions (the AEM Sidekick and this experimental version) enabled at the same time but I recommend to Disable the official one while you are testing the experiment version to avoid any side effect.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fcd9dfa) 89.77% compared to head (ab85603) 89.77%.
Report is 64 commits behind head on main.

Additional details and impacted files

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  Misses        537      537           

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