The LWC server port should be configurable

[trooper2013]

Current implementation has hard coded the port numbers for the LWC server. We need to provide a mechanism to configure the port used during launch of lwc component in the native browser. We should
either employ the use of flags to pass it as an optional to the sfdx plugin or use a config in the sfdx plugin to allow for customization.

[khawkins]

Given that the ownership of the server port configuration lies with the https://github.com/forcedotcom/lwc-dev-server project, ideally we would satisfy this enhancement in a way that encapsulates the responsibility in that project. But if we want to auto-launch the server via the lwc-dev-server plugin interface, we'd still need to provide that input as passthrough configuration, in a manner that's consistent with how it's directly provided to the plugin.