Remove extra hints from tsh app proxies.

[greedy52]

changelog: Fixed an issue tsh aws may display extra text in addition to the original command output

Before:

$ tsh aws sts get-caller-identity
Proxying connections to aws-dev-config on 127.0.0.1:65277
To avoid port randomization, you can choose the listening port using the --port flag.
{
    "UserId": "AROAUBXDPZESRBDQYNUP5:STeve",
    "Account": "278576220453",
    "Arn": "arn:aws:sts::278576220453:assumed-role/steve-poweruser/STeve"
}

$ tsh proxy aws
Proxying connections to aws-dev-config on 127.0.0.1:65153
To avoid port randomization, you can choose the listening port using the --port flag.
Started AWS proxy on http://127.0.0.1:65154.
To avoid port randomization, you can choose the listening port using the --port flag.

Note that the first one breaks jq parsing. Second one is confusing because we showed both 65153 and 65154.

After:

$ tsh aws sts get-caller-identity
{
    "UserId": "AROAUBXDPZESRBDQYNUP5:STeve",
    "Account": "278576220453",
    "Arn": "arn:aws:sts::278576220453:assumed-role/steve-poweruser/STeve"
}

$ tsh proxy aws
Started AWS proxy on http://127.0.0.1:65190.
To avoid port randomization, you can choose the listening port using the --port flag.

$ tsh proxy app redis-tcp
Proxying connections to redis-tcp on 127.0.0.1:65217
To avoid port randomization, you can choose the listening port using the --port flag.

Couldn't find a good/easy way to unit test this. Any suggestion is welcome.

[greedy52]

These were removed so just adding them back.

[public-teleport-github-review-bot]

@greedy52 See the table below for backport results.

Branch	Result
branch/v16	Create PR