feat: improved error message for ssh on invalid environment name

[jackwrfuller]

Description

Closes #457.

This PR introduces a new function environmentCheck() that checks a given environment name string belongs to a project, and if not, returns an error with valid options that the user has access to.

This PR only adds the check to the ssh command, but could be used for any command that mandates a project/environment input.

[shreddedbacon]

#457 (comment)

[shreddedbacon]

In a lot of cases, the API should handle reporting if the environment doesn't exist, for SSH this is a bit different as it doesn't use the API directly.

The main difference here is that SSH portals exist, so for the CLI to know which portal endpoint to use, we have to check if the environment exists to get the portal endpoint it has associated to it.

So the check to get all the environments is already done, this function does it earlier though but it means you're doing two calls to the API every time you run an SSH command.