Introduce new `create-new-microsite` script and update site template

[timonrey]

Description of changes This PR adds a new script called create-new-microsite to create new microsite in the kit. It also updates the site template to bring it to the latest version of our site configuration. Some maintenance and improvements were made as well.

Link to original ticket is part of #2065

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Latest commit: abdd6ba90319c79a808b835bc629b7d1e355a195

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🚚 Build Process Details

Preview URLs:

• https://docskit-tt-bring-site-template-up-to-date.commercetools.vercel.app (permalink to the last build of this branch)
• https://docskit-sha-b85168ff6e3ac9e517c3a741dcd8dbcba22a3b30.commercetools.vercel.app (this commit)