Add production website, update staging

[vgeorge]

In preparation for the presentation at SotM US 2024, it would be nice to setup a production URL for the website and rename the staging URL.

To do:

• decide which URL to use for the production website
• add workflow to deploy the main branch to production
• update workflow to deploy the develop branch to staging
• rename staging URL to osm-gradient.surge.sh

cc @kamicut

[vgeorge]

The CI is configured now to deploy the staging website to https://osm-gradient.surge.sh.

cc @kamicut @willemarcel

[kamicut]

Addressed using new preview and deploy workflow ymls