Support Podman style of accessing the host network in Cypress tests (#11421)

* Supply '--network slirp4netns:allow_host_loopback=true' argument when launching via Podman

This means that the host.containers.internal address will work as a way
to access the host machine's network from within the container in
Podman. This is eqivalent to '--add-host
host.docker.internal:host-gateway' in Docker.

* Log the locations of generated files for Cypress tests

* Use 'host.containers.internal' to access the host network when using Podman

* Support Podman in email Cypress tests too

* Restrict code that decides between Docker and Podman to run in Cypress plugins

Because it can't run in the browser - it needs to run a command line
command to find out.

* Move logic for HOST_DOCKER_INTERNAL into cfgDirFromTemplate

cypress/plugins/docker/index.ts

@@ -156,6 +156,14 @@ export function isPodman(): Promise<boolean> {
     });
 }
 
+/**
+ * Supply the right hostname to use to talk to the host machine. On Docker this
+ * is "host.docker.internal" and on Podman this is "host.containers.internal".
+ */
+export async function hostContainerName() {
+    return (await isPodman()) ? "host.containers.internal" : "host.docker.internal";
+}
+
 /**
  * @type {Cypress.PluginConfig}
  */