Go: Add formatPkg function for custom Go templates

[spinillos]

Custom templates could import packages that aren't defined in the main cue file. This change adds the functionality to the template to add the import in the final result.

[github-actions]

Note: the diff show code changes that would be introduced by this PR to the output of the config/foundation_sdk.dev.yaml codegen pipeline (dev version of the Foundation SDK).

🔎 Changes to config/foundation_sdk.dev.yaml

diff --new-file --unidirectional-new-file '--color=never' --unified --recursive '--exclude=.git' '--exclude=gradle.properties' '--exclude=pyproject.toml' '--exclude=package.json' '--exclude=*.md' /tmp/foundation-workspace-main/foundation-sdk/java/src/main/java/com/grafana/foundation/azuremonitor/BuilderQueryEditorOperatorTypeDeserializer.java /tmp/foundation-workspace-current/foundation-sdk/java/src/main/java/com/grafana/foundation/azuremonitor/BuilderQueryEditorOperatorTypeDeserializer.java
--- /tmp/foundation-workspace-main/foundation-sdk/java/src/main/java/com/grafana/foundation/azuremonitor/BuilderQueryEditorOperatorTypeDeserializer.java	2025-07-14 14:44:33.838360922 +0000
+++ /tmp/foundation-workspace-current/foundation-sdk/java/src/main/java/com/grafana/foundation/azuremonitor/BuilderQueryEditorOperatorTypeDeserializer.java	2025-07-14 14:43:58.171446411 +0000
@@ -17,6 +17,8 @@
 
 import com.grafana.foundation.cog.variants.Dataquery;
 import com.grafana.foundation.cog.variants.Registry;
+import com.grafana.foundation.dashboard.DataSourceRef;
+import com.grafana.foundation.cog.variants.PanelConfig;
 
 
 import java.io.IOException;

[K-Phoen]

Why not sticking with existing helper names?
See the builder.go jenny:

cog/internal/jennies/golang/builder.go

Lines 102 to 104 in 08b3544

	"importStdPkg": func(pkg string) string {
	return imports.Add(pkg, pkg)
	},