Asset building: replace laravel-mix with esbuild

[verheyenkoen]

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[verheyenkoen]

@mietcls Can you review the changed scss files from this PR plz? Does this include any files that you would overwrite when applying theme updates? Especially the fixes for the tagify styles were necessary. These are on old line numbers 549-550 and new line numbers 588-589. I couldn't find where this file originated from. This "bug" was never in the history from the tagify library, unless they purged it maybe.

Also currently there's one deprecation warning during build because a dependency from bootstrap uses the abs() function with a percentage. This has already been fixed in the latest bootstrap version so this would probably disappear on the next update.

[verheyenkoen]

Some manual sass fixes need to be backported to the prototype repo.

[verheyenkoen]

Also sent images through ImageOptim which reduced the buindle size with about 200Kb (20%).