Documentation: List of model configuration keys

[cjohnston1158]

Docs page: https://juju.is/docs/juju/list-of-model-configuration-keys

Docs source: https://discourse.charmhub.io/t/list-of-model-configuration-keys/7068

Issue:

• snap-https-proxy* - link to offline mode strategies doesn't work
• snap-http-proxy* and snap-https-proxy* differ in definitions, though I believe that they should be essentially the same definition
• snap-store-assertions - The definition for this is poorly worded, and I believe incorrect: "snap-store-assertions is the HTTPS proxy value to for installing snaps."
• snap-store-proxy* I believe that this should be the store ID. It would be nice if this was made clearer.
• There are asterisks on the page, indicating that there should be some sort of footnotes available on the page that I'm not seeing.