Allow enable Prometheus metrics on managed tunnel container

[ChrispyBacon-dev]

Allow a configuration setting that tells DockFlare to enable the Prometheus metrics endpoint on the managed tunnel container (i.e. add the --metrics IP:PORT flag).

Example in Docker Compose:

services:
app:
image: cloudflare/cloudflared:latest
restart: unless-stopped
command: tunnel --metrics 0.0.0.0:1234 --no-autoupdate run --token ${TOKEN}
This will allow us to collect metrics from the Cloudflare Tunnel that we can visualise in tools such as Grafana.

#107

[rm-hull]

This would be a very useful addition. I’d be happy to get involved and create a PR for this feature?

[ChrispyBacon-dev]

Hi , thank you,
It is already implemented in the unstable branch. But I want to test it further before PR to stable branch, you can already test it (unstable tag docker image).

new .env ->

# If set to a valid port number (e.g., 2000), enables the Prometheus metrics 
# endpoint on the managed cloudflared agent. The container port will be exposed 
# to the host on the same port number. If left unset or blank, it is disabled.
CLOUDFLARED_METRICS_PORT=

[ChrispyBacon-dev]

feature added ->
https://github.com/ChrispyBacon-dev/DockFlare/releases/tag/v1.9.1
Updated WikI and documentation as well. Tested and created example Grafana Dashboard