ssh: Add `--shell` flag on SSH command to switch between `shell` & `exec` mode

[t1m0thyj]

Is your feature or enhancement request related to a problem or limitation? Please describe

As someone who automates SSH commands with Zowe CLI, I would like an option to disable logging in and running user profile scripts, so that my commands can run faster and more consistently across systems.

Describe your enhancement idea

Add a --shell option to the zowe uss issue ssh command which defaults to true to keep current behavior.
When set to false, then use exec method from ssh2 package instead of shell to issue the command.

Describe alternatives you've considered

Use ssh directly if the zowe uss issue ssh command doesn't satisfy my needs.

Provide any additional context

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