Map Block: Add an option to render map as a static image

#### Is your feature request related to a problem? Please describe.
Even a single Map block element loads relatively large amounts of assets on the front-end, uses a lot of CPU and spawns several worker threads. There is no "static" map block / option available.

Average desktop numbers for the stock `twentytwenty` theme installation and a single post page **with** and **without** the Jetpack Map Block on the page:

* Lighthouse score (without): ~60.
* Lighthouse score (with): ~11.
* Scripting time (without): ~330 ms
* Scripting time (with): ~1100 ms
* Worker threads (without): 0
* Worker threads (with): 8
* Network transfer (without): 0.8 MB
* Network transfer (with): 1.9 MB

#### Describe the solution you'd like
Assuming that not all users of the Map block _need_ an interactive map on their site, an option to render a map as an image using the [Mapbox Static Image API](https://docs.mapbox.com/api/maps/#static-images) could noticeably improve performance.

The static image could also serve as a placeholder while the interactive experience is being loaded (maybe the initialization can happen lazily based on viewport position; maybe the user can trigger the interactive experience by clicking / tapping the static image).

The API [supports markers](https://docs.mapbox.com/api/maps/#marker) in static images. I'd suggest adding an option to the Block settings that would allow authors to not load the whole Mapbox runtime and only display a pre-generated map image instead. Something like **Interactive:** Yes; On click / tap; No.

#### Additional context / considerations / ideas
**Pricing:** Opportunity to provide more value. Mapbox's free tier [allows for 50,000 map loads](https://www.mapbox.com/pricing/#maploads) per month and also up to [50,000 Static Image API hits](https://www.mapbox.com/pricing/#glstatic). By fetching and storing a static representation of the map, we would only consume the quota (Static API quota) when a static image is generated / regenerated or when the user opts for the interactive experience (map load quota).

**Save-Data**: Feels like not-initializing a full map experience when the [`Save-Data`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Save-Data) header is `on` could be a good idea.

**Responsiveness**: Currently the block changes its width on the front end to fit on the page. This may not be ideal for static images.