Install snaps with devmode in end-to-end tests (#7343)

Following a recent fix in our snap packages, our end-to-end tests started to fail. The tests need to install the azure-iot-edge snap with --devmode, at least until we get approval to auto-connect the daemon-notify interface (in progress).

This change updates the install command in the end-to-end tests to prevent failures. I ran the end-to-end test pipeline and confirmed this fixes the failures.

## Azure IoT Edge PR checklist:

test/Microsoft.Azure.Devices.Edge.Test.Common/linux/PackageManagement.cs

@@ -73,7 +73,7 @@ public string[] GetInstallCommandsFromLocal(string path)
                 SupportedPackageExtension.Snap => new[]
                 {
                     "set -e",
-                    $"snap install {string.Join(' ', packages)} --dangerous",
+                    $"snap install {string.Join(' ', packages)} --dangerous --devmode",
                     "snap connect azure-iot-identity:hostname-control",
                     "snap connect azure-iot-identity:log-observe",
                     "snap connect azure-iot-identity:mount-observe",