[3007.x] Fix Salt-SSH loader attribute access, document that it's still not recommended

[lkubb]

What does this PR do?

• Ensures the FunctionWrapper used in Salt-SSH templates behaves more like the regular LazyLoader
• Adjusts documentation that salt['foo.bar']() is to be preferred over salt.foo.bar() since the latter can introduce edge cases

What issues does this PR fix or reference?

Fixes: https://github.com/saltstack/salt/issues/41794 Fixes: https://github.com/saltstack/salt/issues/66376 Fixes: https://github.com/saltstack/salt/issues/66600

Previous Behavior

Several issues when using the salt.foo.bar syntax (see linked issues)

New Behavior

Works as expected. There might be some unknown edge cases though, so still prefer salt['foo.bar'].

Merge requirements satisfied?

• [x] Docs
• [x] Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• [x] Tests written/updated

Commits signed with GPG?

Yes