buildx: install method

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

__tests__/buildx/buildx.test.ts

@@ -88,6 +88,14 @@ describe('certsDir', () => {
   });
 });
 
+describe('install', () => {
+  it('acquires buildx v0.9.1', async () => {
+    const buildx = new Buildx({context: new Context()});
+    const buildxBin = await buildx.install('v0.9.1', tmpDir);
+    expect(fs.existsSync(buildxBin)).toBe(true);
+  }, 100000);
+});
+
 describe('isAvailable', () => {
   it('docker cli', async () => {
     const execSpy = jest.spyOn(exec, 'getExecOutput');

src/buildx/buildx.ts

@@ -34,16 +34,16 @@ export interface BuildxOpts {
 export class Buildx {
   private readonly context: Context;
   private _version: string | undefined;
+  private _install: Install;
 
   public readonly inputs: Inputs;
-  public readonly install: Install;
   public readonly standalone: boolean;
 
   constructor(opts: BuildxOpts) {
     this.context = opts.context;
     this.inputs = new Inputs(this.context);
-    this.install = new Install({standalone: opts.standalone});
     this.standalone = opts?.standalone ?? !Docker.isAvailable;
+    this._install = new Install({standalone: opts.standalone});
   }
 
   static get configDir(): string {
@@ -61,6 +61,10 @@ export class Buildx {
     };
   }
 
+  public async install(version: string, dest: string): Promise<string> {
+    return await this._install.install(version, dest);
+  }
+
   public async isAvailable(): Promise<boolean> {
     const cmd = this.getCommand([]);
     return await exec