Add gradle samples in maven doc of packages (#23374)

Samples for gitea.io docs to help to use maven packages with
gradle-oriented projects

---------

Co-authored-by: KN4CK3R <admin@oldschoolhack.me>

docs/content/doc/packages/maven.en-us.md

@@ -23,7 +23,7 @@ Publish [Maven](https://maven.apache.org) packages for your user or organization
 ## Requirements
 
 To work with the Maven package registry, you can use [Maven](https://maven.apache.org/install.html) or [Gradle](https://gradle.org/install/).
-The following examples use `Maven`.
+The following examples use `Maven` and `Gradle Groovy`.
 
 ## Configuring the package registry
 
@@ -73,6 +73,40 @@ Afterwards add the following sections to your project `pom.xml` file:
 | `access_token` | Your [personal access token]({{< relref "doc/developers/api-usage.en-us.md#authentication" >}}). |
 | `owner`        | The owner of the package. |
 
+### Gradle variant
+
+When you plan to add some packages from Gitea instance in your project, you should add it in repositories section:
+
+```groovy
+repositories {
+    // other repositories
+    maven { url "https://gitea.example.com/api/packages/{owner}/maven" }
+}
+```
+
+In Groovy gradle you may include next script in your publishing part:
+
+```groovy
+publishing {
+    // other settings of publication
+    repositories {
+        maven {
+            name = "Gitea"
+            url = uri("https://gitea.example.com/api/packages/{owner}/maven")
+
+            credentials(HttpHeaderCredentials) {
+                name = "Authorization"
+                value = "token {access_token}"
+            }
+
+            authentication {
+                header(HttpHeaderAuthentication)
+            }
+        }
+    }
+}
+```
+
 ## Publish a package
 
 To publish a package simply run:
@@ -81,6 +115,12 @@ To publish a package simply run:
 mvn deploy
 ```
 
+Or call `gradle` with task `publishAllPublicationsToGiteaRepository` in case you are using gradle:
+
+```groovy
+./gradlew publishAllPublicationsToGiteaRepository
+```
+
 If you want to publish a prebuild package to the registry, you can use [`mvn deploy:deploy-file`](https://maven.apache.org/plugins/maven-deploy-plugin/deploy-file-mojo.html):
 
 ```shell
@@ -105,6 +145,12 @@ To install a Maven package from the package registry, add a new dependency to yo
 </dependency>
 ```
 
+And analog in gradle groovy:
+
+```groovy
+implementation "com.test.package:test_project:1.0.0"
+```
+
 Afterwards run:
 
 ```shell