Remove the `permanent` field from redirects in `config.json`

[ptgott]

Our legacy docs engine expected the redirects declared in config.json within each gravitational/teleport submodule to have a permanent field, but Docusaurus redirects do not require this. Let's remove the permanent field, since it is unnecessary and often leads to merge conflicts when we update the redirects configuration.

Note that, as part of this, we should make sure that the docpaths workflow we run to check redirects introduced by PRs can accommodate redirect configurations without the permanent field.