Initialize Teleport and exit

[russjones]

Problem

To install Teleport on a server at the moment you have to do the following.

1. Add the provisioning token to teleport.yaml or pass it on the command line.
2. Start Teleport and wait for /var/lib/teleport to be initialized.
3. Shut down Teleport.
4. Remove the token from either teleport.yaml or command line.
5. Star Teleport.

While not difficult to script, it is a bit cumbersome.

Proposed Solution

Teleport should support an "initialize mode" where the token can be passed in using a environment variable or read in from a file on disk. Teleport would read in the provisioning token, initialize /var/lib/teleport and quit.

Then Teleport can be started without the token as it normally would.

[kontsevoy]

note to self: lets talk to a user who requested this feature. need more context

[klizhentas]

Use SSM parameter store ticket, dupe of #1546