fix(web): import builtin plugin from external url

[keiya01]

Overview

I tried to fix the unsafe builtin plugin system to load the built-in plugin from outside the repository to be more independent.

What I've done

What I haven't done

How I tested

1. Download builtin-plugin-example.zip
2. Move to above file
3. yarn && yarn dev
4. Move to reearth/server
5. Set REEARTH_EXT_PLUGIN=http://localhost:5001 in .env for server
6. Move to reearth/web
7. Set REEARTH_WEB_UNSAFE_PLUGIN_URLS='["http://localhost:5001/Example.js"]' in .env for web
8. yarn start
9. Open Beta project
10. Go to widget page
11. Add the widget named Extension

Which point I want you to review particularly

Memo

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[codecov]

Codecov Report

Merging #625 (cf8314e) into main (d196904) will increase coverage by 0.00%.
The diff coverage is 23.33%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #625   +/-   ##
=======================================
  Coverage   28.43%   28.43%           
=======================================
  Files        1457     1456    -1     
  Lines      158416   158419    +3     
  Branches     3764     3763    -1     
=======================================
+ Hits        45043    45047    +4     
+ Misses     112216   112215    -1     
  Partials     1157     1157           

Flag	Coverage Δ
web	26.52% <23.33%> (+<0.01%)	⬆️
web-beta	26.52% <23.33%> (+<0.01%)	⬆️
web-classic	26.52% <23.33%> (+<0.01%)	⬆️
web-utils	26.52% <23.33%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
...b/core/Crust/Infobox/Block/builtin/unsafeBlocks.ts	42.42% <0.00%> (+3.03%)	⬆️
...core/Crust/Widgets/Widget/builtin/unsafeWidgets.ts	0.00% <0.00%> (ø)
web/src/services/config/index.ts	66.66% <20.00%> (-0.99%)	⬇️
web/src/services/config/unsafeBuiltinPlugin.ts	63.88% <31.57%> (-3.86%)	⬇️