Remove shortname from preview installations

Use `yq -m` to merge an inline config rather than `yq -w` because the
old version of `yq` we have installed does not support setting fields to
the empty string literal.

Author: Andrew Farries

.werft/jobs/build/installer/installer.ts

@@ -58,6 +58,7 @@ export class Installer {
         this.options.werft.log(slice, "Adding extra configuration");
         try {
             this.getDevCustomValues(slice)
+            this.configureMetadata(slice)
             this.configureContainerRegistry(slice)
             this.configureDomain(slice)
             this.configureWorkspaces(slice)
@@ -94,6 +95,14 @@ export class Installer {
         exec(`yq m -i ${this.options.installerConfigPath} ${WORKSPACE_SIZE_CONFIG_PATH}`, { slice: slice });
     }
 
+    private configureMetadata(slice: string): void {
+        exec(`cat <<EOF > shortname.yaml
+metadata:
+  shortname: ""
+EOF`)
+        exec(`yq m -ix ${this.options.installerConfigPath} shortname.yaml`, { slice: slice });
+    }
+
     private configureContainerRegistry(slice: string): void {
         exec(`yq w -i ${this.options.installerConfigPath} certificate.name ${this.options.proxySecretName}`, { slice: slice });
         exec(`yq w -i ${this.options.installerConfigPath} containerRegistry.inCluster false`, { slice: slice });