feat: suppress Maven transfer progress via MAVEN_ARGS by default

Set MAVEN_ARGS to include -ntp (--no-transfer-progress) so Maven invocations
in the job produce cleaner CI logs without download/transfer progress noise.
Add a new optional 'show-download-progress' input (default false); set it to
true to keep the progress output.

The change preserves any existing MAVEN_ARGS value (the flag is appended,
not overwritten) and is idempotent (it won't add the flag twice if -ntp or
--no-transfer-progress is already present). Applies on all platforms; honored
by Maven 3.9.0+ and the Maven Wrapper, and is a no-op for non-Maven builds.

- action.yml: add show-download-progress input
- src/constants.ts: add input + MAVEN_ARGS constants
- src/maven-args.ts: new configureMavenArgs()
- src/setup-java.ts: invoke configureMavenArgs() during setup
- __tests__/maven-args.test.ts: unit tests
- docs/advanced-usage.md: document the behavior and input
- dist: rebuild bundled action

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

__tests__/maven-args.test.ts

@@ -0,0 +1,104 @@
+import * as core from '@actions/core';
+
+import {configureMavenArgs} from '../src/maven-args';
+import {
+  INPUT_SHOW_DOWNLOAD_PROGRESS,
+  MAVEN_ARGS_ENV,
+  MAVEN_NO_TRANSFER_PROGRESS_FLAG
+} from '../src/constants';
+
+describe('configureMavenArgs', () => {
+  let inputs: Record<string, string>;
+  let spyGetInput: jest.SpyInstance;
+  let spyExportVariable: jest.SpyInstance;
+  let spyInfo: jest.SpyInstance;
+  let spyDebug: jest.SpyInstance;
+  const originalMavenArgs = process.env[MAVEN_ARGS_ENV];
+
+  beforeEach(() => {
+    inputs = {};
+
+    spyGetInput = jest.spyOn(core, 'getInput');
+    spyGetInput.mockImplementation((name: string) => inputs[name] ?? '');
+
+    spyExportVariable = jest.spyOn(core, 'exportVariable');
+    spyExportVariable.mockImplementation((name: string, value: string) => {
+      process.env[name] = value;
+    });
+
+    spyInfo = jest.spyOn(core, 'info');
+    spyInfo.mockImplementation(() => undefined);
+
+    spyDebug = jest.spyOn(core, 'debug');
+    spyDebug.mockImplementation(() => undefined);
+
+    delete process.env[MAVEN_ARGS_ENV];
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks();
+    if (originalMavenArgs === undefined) {
+      delete process.env[MAVEN_ARGS_ENV];
+    } else {
+      process.env[MAVEN_ARGS_ENV] = originalMavenArgs;
+    }
+  });
+
+  it('sets MAVEN_ARGS with -ntp by default', () => {
+    configureMavenArgs();
+
+    expect(spyExportVariable).toHaveBeenCalledWith(
+      MAVEN_ARGS_ENV,
+      MAVEN_NO_TRANSFER_PROGRESS_FLAG
+    );
+    expect(process.env[MAVEN_ARGS_ENV]).toBe(MAVEN_NO_TRANSFER_PROGRESS_FLAG);
+  });
+
+  it('does not modify MAVEN_ARGS when show-download-progress is true', () => {
+    inputs[INPUT_SHOW_DOWNLOAD_PROGRESS] = 'true';
+
+    configureMavenArgs();
+
+    expect(spyExportVariable).not.toHaveBeenCalled();
+    expect(process.env[MAVEN_ARGS_ENV]).toBeUndefined();
+  });
+
+  it('preserves an existing MAVEN_ARGS value and appends -ntp', () => {
+    process.env[MAVEN_ARGS_ENV] = '-B -Dstyle.color=always';
+
+    configureMavenArgs();
+
+    expect(spyExportVariable).toHaveBeenCalledWith(
+      MAVEN_ARGS_ENV,
+      `-B -Dstyle.color=always ${MAVEN_NO_TRANSFER_PROGRESS_FLAG}`
+    );
+  });
+
+  it('does not duplicate the flag when -ntp is already present', () => {
+    process.env[MAVEN_ARGS_ENV] = '-B -ntp';
+
+    configureMavenArgs();
+
+    expect(spyExportVariable).not.toHaveBeenCalled();
+    expect(process.env[MAVEN_ARGS_ENV]).toBe('-B -ntp');
+  });
+
+  it('does not duplicate the flag when --no-transfer-progress is already present', () => {
+    process.env[MAVEN_ARGS_ENV] = '--no-transfer-progress -B';
+
+    configureMavenArgs();
+
+    expect(spyExportVariable).not.toHaveBeenCalled();
+    expect(process.env[MAVEN_ARGS_ENV]).toBe('--no-transfer-progress -B');
+  });
+
+  it('keeps the existing MAVEN_ARGS when show-download-progress is true', () => {
+    inputs[INPUT_SHOW_DOWNLOAD_PROGRESS] = 'true';
+    process.env[MAVEN_ARGS_ENV] = '-B';
+
+    configureMavenArgs();
+
+    expect(spyExportVariable).not.toHaveBeenCalled();
+    expect(process.env[MAVEN_ARGS_ENV]).toBe('-B');
+  });
+});