[http][doc] improve v2 Access Control List docs

Came across this issue #928 while trying to set up a v2 app. I think this an opportunity to improve the documentation, as after reading through the capabilities/permissions setup docs several times I'm still not able to get a buildable application.

Some examples of how it can be improved:

1) Include a real-world example that uses http fetch from both a localhost api and a remote api server
2) visual file hierarchy image
3) At https://beta.tauri.app/references/v2/acl/#remote-access there is a random ellipsis just placed into the permissions array, with no indication or examples as to what should go in there. As a rule of thumb, no documentation that has a "copy" button with the intention of being put into an IDE or editor, should ever have syntax errors, like this does.
4) At https://beta.tauri.app/references/v2/acl/#target-platform
```
"permissions": ["global-shortcut:allow-register"]
```

this permission doesn't exist. Why was it included in the docs?

In addition, both the npm and cargo plugin add commands should be able to scaffold these permissions/capabilities automatically, but that is another issue in another repo.