Manifest-url-only install. Perhaps standard .well-known/manifest.webmanifest

[dmurph]

This has come up over the years, and with the idea of an install element that would need a not-terrible way of fetching app information, I thought we could revisit this.

We can go over why we haven't done this in the past, ways that it might be possible, and other thoughts.

One crazy idea:

• Formalize that an origin can specify a .well-known/manifest.webmanifest file. If this exists, then the user agent can find it from an origin.
• Add (back?) the serviceworker member to the manifest, to allow user agents to install & activate a serviceworker when install occurs, to allow the dev to offline any content needed for the site to launch while offline.

Obviously some pros & cons there.