Hide Koding setting in admin panel if not enabled

Closes #30162

See merge request !13992

Add settings for minimum key strength and allowed key type

Closes #17849

See merge request !13712

Rollback changes made to signing_enabled.

Closes #37202

See merge request !13956

Resolve various visibility level settings issues

Closes #31273

See merge request !13442

`allowed_key_types` is removed and the `minimum_<type>_bits` fields are
renamed to `<tech>_key_restriction`. A special sentinel value (`-1`) signifies
that the key type is disabled.

This also feeds through to the UI - checkboxes per key type are out, inline
selection of "forbidden" and "allowed" (i.e., no restrictions) are in.

As with the previous model, unknown key types are disallowed, even if the
underlying ssh daemon happens to support them. The defaults have also been
changed from the lowest known bit size to "no restriction". So if someone
does happen to have a 768-bit RSA key, it will continue to work on upgrade, at
least until the administrator restricts them.

This is an amalgamation of:

* Cory Hinshaw: Initial implementation !5552
* Rémy Coutable: Updates !9350
* Nick Thomas: Resolve conflicts and add ED25519 support !13712

Move ConvDev Index location to after Cohorts

Closes #34413

See merge request !13398