feat(new): add Related Resources source link to builtin rule doc template (#1957)

Builtin rule docs scaffolded by `regal new rule --type builtin` now
include a Related Resources section pointing at the rule's .rego file
on GitHub, matching the pattern in existing rule docs.

Part of #1567

Signed-off-by: Matt Van Horn <mvanhorn@gmail.com>

Author: mvanhorn

cmd/new.go

@@ -35,6 +35,7 @@ type TemplateValues struct {
 	NameOriginal string
 	Name         string
 	NameTest     string
+	FileName     string
 }
 
 var (
@@ -257,6 +258,7 @@ func createBuiltinDocs(params newRuleCommandParams) error {
 func templateValues(params newRuleCommandParams) (tvs TemplateValues) {
 	tvs.Category = params.category
 	tvs.NameOriginal = params.name
+	tvs.FileName = strings.ToLower(strings.ReplaceAll(params.name, "-", "_")) + ".rego"
 
 	if strings.Contains(params.name, "-") || strings.Contains(params.name, "_") {
 		dashedNameValue := strings.ReplaceAll(params.name, "_", "-")

internal/embeds/templates/builtin/builtin.md.tpl

@@ -35,3 +35,7 @@ rules:
       # one of "error", "warning", "ignore"
       level: error
 ```
+
+## Related Resources
+
+- GitHub: [Source Code](https://github.com/open-policy-agent/regal/blob/main/bundle/regal/rules/{{.Category}}/{{.NameOriginal}}/{{.FileName}})