Make Signal Service listen on a standard 443/80 port instead of 10000

[braginini]

This PR is a part of an effort to use standard ports (443 or 80) that are usually allowed by default in most of the environments.

Right now Signal Service runs the Let'sEncrypt manager on port 443
and a gRPC server on port 10000. There are two separate listeners.
This PR combines these listeners into one
With this change, the gRPC server runs on either 443 with TLS or 80 without TLS
by default (no --port specified).
Let's Encrypt manager always runs on port 443 if enabled.
The backward compatibility server runs on port 10000 (with TLS or without).

Agents that are running and on status Online will still be connected to 10000.
Triggering Agent restart of any version will force it to connect to port 443.

[braginini]

1. TLS enabled, --port=10000 (equals to previous versions).

./signal run --log-level debug --log-file console --letsencrypt-domain test.wiretrustee.com --port 10000

No multiplexing, HTTP, and gRPC are running on separate ports - 443 and 10000 respectively:

time="2022-07-24T17:03:59+02:00" level=info msg="running with LetsEncrypt (test.wiretrustee.com). Cert will be stored in /var/lib/netbird/letsencrypt" file="letsencrypt.go:21"
time="2022-07-24T17:03:59+02:00" level=info msg="running gRPC server: [::]:10000" file="run.go:225"
time="2022-07-24T17:03:59+02:00" level=info msg="running HTTP server: [::]:443" file="run.go:198"
time="2022-07-24T17:03:59+02:00" level=info msg="started Signal Service" file="run.go:157"

2. TLS enabled, --port is not specified.

run --log-level debug --log-file console --letsencrypt-domain test.wiretrustee.com

Multiplexing. HTTP and gRPC sharing port 443. Compatibility gRPC server runs on 10000:

time="2022-07-24T17:12:00+02:00" level=info msg="running with LetsEncrypt (test.wiretrustee.com). Cert will be stored in /var/lib/netbird/letsencrypt" file="letsencrypt.go:21"
time="2022-07-24T17:12:00+02:00" level=info msg="running gRPC backward compatibility server: [::]:10000" file="run.go:214"
time="2022-07-24T17:12:00+02:00" level=info msg="running gRPC server: [::]:443" file="run.go:225"
time="2022-07-24T17:12:00+02:00" level=info msg="running HTTP server: [::]:443" file="run.go:198"
time="2022-07-24T17:12:00+02:00" level=info msg="running gRPC and HTTP server in a multiplex mode on port 443" file="run.go:188"
time="2022-07-24T17:12:00+02:00" level=info msg="started Signal Service" file="run.go:157"

3. TLS disabled, --port is not specified

run --log-level debug --log-file console

No multiplexing. The HTTP server isn't running. gRPC server runs on 80. Compatibility gRPC server runs on 10000:

time="2022-07-24T17:14:42+02:00" level=info msg="running gRPC backward compatibility server: [::]:10000" file="run.go:214"
time="2022-07-24T17:14:42+02:00" level=info msg="running gRPC server: [::]:80" file="run.go:225"
time="2022-07-24T17:14:42+02:00" level=info msg="started Signal Service" file="run.go:157"

4. TLS disabled, --port=10000 (equals to previous versions):

run --log-level debug --log-file console --port 10000

No multiplexing. The HTTP server isn't running. A single gRPC server runs on 10000:

time="2022-07-24T17:18:13+02:00" level=info msg="running gRPC server: [::]:10000" file="run.go:225"
time="2022-07-24T17:18:13+02:00" level=info msg="started Signal Service" file="run.go:157"