tsh play should take a file argument as a valid parameter

[kontsevoy]

Problem

If a user periodically backs up recorded sessions to a long-term storage (like Glacier) and decides to replay a sessions from 2 years ago, there is no easy way to do this in Teleport right now.

Solution

Currently a recorded session is a set of files:

• session stream file(s) - they have the same name prefix, possibly compressed
• session events file
• (optional) cryptographic signature file Support gzip for session recording #1579

So if a session stream files are named:

2394827492384723-x.gz 
2394827492384723-y.gz 
2394827492384723-z.gz 
2394827492384723.json  # events
2394827492384723.pem  # SSH signature 

Then all of the following should work:

$ tsh play ./2394827492384723-y.gz
$ tsh play 2394827492384723

And if the .pem file is missing or invalid, a warning should be shown:

WARNING: cluster signature is missing for session 2394827492384723
WARNING: cluster signature is INVALID for session 2394827492384723

[klizhentas]

it should actually take our tarball format as is and play it instead, this way folks can download and play all tarballs sent to S3 for example

[klizhentas]

@kontsevoy I suggest we move this one out of 2.6.0 to reduce the scope a bit, does not seem like a pressing issue.

[benarent]

This came up again today during an evaluation. +1 for providing tsh play to support working with the tarball format.

[webvictim]

Another request for this in #3225

[travelton]

Another request in ZD#1699. Building some sort of index from stored objects would be helpful to locate the sessions of interest. The events object contains the session metadata.