Cloud customers should use port 443 when configuring agents

[bpdohall]

Updating various docs to specify use of port 443 when setting up Teleport Agents.

When port is omitted, the agent goes into a retry loop as the default port (3025) is not available via a cloud tenant's subdomain.

$ sudo teleport db start --token=abcdefghijklmnopqrstuvwxyz012345 --auth-server=brendan.cloud.gravitational.io --name=pgdocker --protocol=postgres --uri=postgres.db.local:5432
INFO [PROC:1]    Connecting to the cluster brendan.cloud.gravitational.io with TLS client certificate. service/connect.go:164
ERRO [PROC:1]    Failed to resolve tunnel address Get "https://brendan.cloud.gravitational.io:3025/webapi/find": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers) reversetunnel/transport.go:90
ERRO [PROC:1]    "Db failed to establish connection to cluster: Failed to connect to Auth Server directly or over tunnel, no methods remaining.\n\tGet \"https://teleport.cluster.local/v2/domain\": dial tcp 15.197.198.101:3025: i/o timeout, Get \"https://teleport.cluster.local/v2/domain\": Get \"https://brendan.cloud.gravitational.io:3025/webapi/find\": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers)." service/connect.go:86
ERRO [PROC:1]    Failed to resolve tunnel address Get "https://brendan.cloud.gravitational.io:3025/webapi/find": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers) reversetunnel/transport.go:90

[ptgott]

Approved with a suggestion