Caddy does not support URLs with ports

Description:

Setting caddy-url to a URL with a port does not work.

Steps to reproduce:

1. Try to set the caddy-url:

$ sudo snap set rocketchat-server caddy-url=https://rocket.example.net:8000

Expected behavior:

The URL is accepted.

Actual behavior:

Setting the URL fails with

$ sudo snap set rocketchat-server caddy-url=https://rocket.example.net:8000
error: cannot perform the following tasks:
- Run configure hook of "rocketchat-server" snap (run hook "configure": "https://rocket.example.net:8000"
            is not a valid url)

Server Setup Information:

• Version of Rocket.Chat Server:
• Operating System: Ubuntu 18.03
• Deployment Method: snap
• Number of Running Instances: 1
• DB Replicaset Oplog: NA
• NodeJS Version: NA
• MongoDB Version: NA

Additional context

The issue is contained in the snap configure script where no port is accepted.

https://github.com/RocketChat/Rocket.Chat/blob/119028b17f71df8797a46234cfee7cc6c8ee9217/.snapcraft/snap/hooks/configure#L11

Related Problem

An additional related problem is that when caddy is enabled, changes to siteurl are silently ignored because they are overwritten by caddy-url in the same script: https://github.com/RocketChat/Rocket.Chat/blob/119028b17f71df8797a46234cfee7cc6c8ee9217/.snapcraft/snap/hooks/configure#L51

$ sudo snap get rocketchat-server siteurl
https://rocket.example.net
$ sudo snap set rocketchat-server siteurl=https://my-new-url.example.net
$ sudo snap get rocketchat-server siteurl
https://rocket.example.net

Read .snapcraft/snap/hooks/configure, especially the validation near line 11 and the siteurl handling near line 51. Reproduce the snap set command with a port, then verify that caddy-url accepts it and that siteurl changes behave as expected when Caddy is enabled.