fix(cdk-assets): Docker Build Context Path

Prior v1.29.0, the context passed to the docker build command was always
the current working directory. In v1.29.0, this was changed to be the
directory the user passed when instantiating the asset. However, docker
doesn't respect the context passed to the build command when the
`--file` argument is also passed. This broke assets for users passing
the `file` prop when constructing a `DockerImageAsset`.

This is fixed by changing the current working directory of the `docker build`
command and passing that context as '.'. Then docker uses the current working
directory as the context and correctly finds the image definition file from the
`file` prop. An existing integration test in the framework covers this case,
but does not fail unless the stack is deployed fresh since the asset isn't
rebuilt when the hash is not changed.

Fix: #6954 #6814

packages/cdk-assets/lib/private/docker.ts

@@ -37,9 +37,9 @@ export class Docker {
       '--tag', options.tag,
       ...options.target ? ['--target', options.target] : [],
       ...options.file ? ['--file', options.file] : [],
-      options.directory,
+      '.'
     ];
-    await this.execute(buildCommand);
+    await this.execute(buildCommand, { cwd: options.directory });
   }
 
   /**
@@ -100,4 +100,4 @@ async function obtainEcrCredentials(ecr: AWS.ECR, logger?: Logger) {
 
 function flatten(x: string[][]) {
   return Array.prototype.concat([], ...x);
-}
+}