Document the format for SSH key

[cgardens]

Tell us about the problem you're trying to solve

We have added support for SSH in postgres source and destination. There are some details to generating a correctly formatted SSH key that are not intuitive / easy to mess up. We need to make sure to add them into our docs.

[airbyte-jenny]

Documented in
#6585

Also improved the wording on the connector setup screens, so the ssh-keygen command is available at point of use.

[klogdog]

Airbyte should generate the key. It has the libraries setup to do this and there is no good reason that it cannot generate and store the private key and provide the public key for installs. (Similar services such as Fivetran just provide the public key that is used for install on the egress server)

This should be an integrated feature. SSH key auth should also have a password field for those that wish to password protect their SSH private keys.