Add share moment button for sharing screenshots

[jokroese]

It would be great to make the output more easily shareable.

Some relevant links on how to get the screenshot:

• https://larryhudson.io/protomaps-maplibre-screenshot/
• https://github.com/larryhudson/astro-protomaps-maplibre-screenshot/blob/6627c158774bf0bf4d5c080511136767d1550f50/src/utils/map-utils.ts#L117C13-L129C16
• https://github.com/walpolea/andrewwalpole.com/blob/master/src/pages/preview/%5Bslug%5D.astro
• https://html2canvas.hertzen.com/
• Generating an image from the map canvas results in blank images. maplibre/maplibre-gl-js#3900

[nielsbom]

Is that a feature (many) people asked for?