feat: improve `install` onboarding

[devlsh]

Is your feature request related to a problem? Please describe.

1. Currently when using devon install on macOS 11+ it will just tell you to run a command to manually add the certificate files.
2. devon install will always attempt to install the certificate chain regardless of whether it exists already.

Describe the solution you'd like

1. This shouldn't happen - devon already has the ability to run sudo commands (As it does on Windows/Linux) so it should just run this itself.
2. This also shouldn't happen - it should attempt to check if it already exists. Not entirely sure how - potentially mkcert has some logic for this.

[devlsh]

Will have to wait on FiloSottile/mkcert#332 before this can be added.