Extension docs: npm, bundler, min/unmin and SRI hash instructions

[marisst]

Pull request should be viewed together with the corresponding PR in htmx-extensions repository bigskysoftware/htmx-extensions#123.

Documentation is updated to elaborate on extension installation and integration. Until now, extension installation instructions were limited to a CDN script tag. This change adds:

• guidance on installation with npm
• guidance on integration with bundlers
• instructions to access minified and unminified extension versions
• SRI hash in CDN script tag installation example
• links to newest extension versions which were released with the [email protected] release
• makes the need of hx-ext clearer Extensions documentation could make need for hx-ext clearer #2475