Add `html`/`static` to commands for `rsconnect write-manifest`

[brooklynbagel]

rsconnect deploy has a command for deploying static HTML content to Connect with rsconnect deploy html. There is no equivalent command for rsconnect write-manifest making it difficult to deploy such content using git.

• A manifest.json for static content, https://github.com/brooklynbagel/reflex-pct/blob/0957b519e569b120c3f4514954d54ac8baf2b76c/frontend/manifest.json
• Sample script to generate manifest.json, https://github.com/brooklynbagel/reflex-pct/blob/0957b519e569b120c3f4514954d54ac8baf2b76c/write-manifest.py

[aronatkins]

Similar to https://github.com/posit-dev/rsconnect-python/issues/548