feat(datasource/custom): add `currentValue` to template metadata (#27038)

lib/modules/datasource/custom/readme.md

@@ -16,6 +16,7 @@ Options:
 Available template variables:
 
 - `packageName`
+- `currentValue`
 
 ```json
 {

lib/modules/datasource/custom/utils.ts

@@ -9,6 +9,7 @@ export function massageCustomDatasourceConfig(
   {
     customDatasources,
     packageName,
+    currentValue,
     registryUrl: defaultRegistryUrl,
   }: GetReleasesConfig,
 ): Required<CustomDatasourceConfig> | null {
@@ -19,7 +20,7 @@ export function massageCustomDatasourceConfig(
     );
     return null;
   }
-  const templateInput = { packageName };
+  const templateInput = { packageName, currentValue };
 
   const registryUrlTemplate =
     defaultRegistryUrl ?? customDatasource.defaultRegistryUrlTemplate;

lib/modules/datasource/types.ts

@@ -27,6 +27,7 @@ export interface GetReleasesConfig {
   datasource?: string;
   packageName: string;
   registryUrl?: string;
+  currentValue?: string;
 }
 
 export interface GetPkgReleasesConfig {
@@ -37,6 +38,7 @@ export interface GetPkgReleasesConfig {
   additionalRegistryUrls?: string[];
   datasource: string;
   packageName: string;
+  currentValue?: string;
   versioning?: string;
   extractVersion?: string;
   versionCompatibility?: string;