Joining an active CLI session from Web UI messes with the CLI output

[pschisa]

Expected behavior: Joining an active session as an observer will not impact the active session for the user

Current behavior: When running commands like top on the CLI, if a web UI user joins the session as an observer the output in the CLI is affected and becomes unreadable. This is fixed if the CLI terminal is resized.

https://github.com/gravitational/teleport/assets/75806143/84a81a42-1a55-412e-8d29-b612983f6a98

Bug details:

• Teleport version v15
• Recreation steps Start a session from the CLI run the command top Log into the same cluster in the Web UI join the active session as an observer

[zmb3]

Maybe the flakiness in TestResizeTerminal is pointing at a real issue..

The observer who joins should not be sending a resize sequence, but it looks like they are.