feat: add support for cdnPrefix for static assets

[ivarconr]

note this feature is experimental.

Allows you to specify a cdnPrefix for static resource.

When specified CSS and JavaScript is loaded directly from CDN, like this:

Also replaces a meta tag in the index.html with the cdnPrefix, which may be utilized by the frontend code to use CDN prefix for dynamic static assets, such as images.

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[github-actions]

Coverage report

Total coverage

Status	Category	Percentage	Covered / Total
🟢	Statements	92.06%	4612/5010
🟢	Branches	81.02%	717/885
🟢	Functions	87.84%	1084/1234
🟢	Lines	93.91%	5242/5582

Status of coverage: 🟢 - ok, 🟡 - slightly more than threshold, 🔴 - under the threshold

Show new covered files 🌑

Coverage of new files

Status	Filename	Statements	Branches	Functions	Lines
🟢	src/lib/util/load-index-html.ts	81.82%	33.33%	100%	100%

Status of coverage: 🟢 - ok, 🟡 - slightly more than threshold, 🔴 - under the threshold

Show files with reduced coverage 🔻

Reduced coverage

Status	Filename	Statements	Branches	Functions	Lines
🟢	src/lib/app.ts	81.48%	68.42%	66.67%	92.96%

Status of coverage: 🟢 - ok, 🟡 - slightly more than threshold, 🔴 - under the threshold

Report generated by 🧪jest coverage report action from b70cfa0

[ivarconr]

Will not solve dynamically loaded assets:

[FredrikOseberg]

Very cool. LGTM.