StacBrowser construct doesn't prefix S3 keys when pathPrefix is set

[botanical]

When pathPrefix is set on the StacBrowser construct, the build correctly bakes the prefix into the app's publicPath but I think the files in BucketDeployment get uploaded to the root regardless of what pathPrefix is set to.

We have to rewrite the path downstream in order to properly serve anything in the bucket behind the prefix path.

so the proposed change would be something like:

        this.bucketDeployment = new s3_deployment.BucketDeployment(this, 'BucketDeployment', {
            destinationBucket: this.bucket,
            destinationKeyPrefix: props.pathPrefix?.replace(/^\/+|\/+$/g, ''),
            sources: [s3_deployment.Source.asset(buildPath)],
            memoryLimit: 1024,
            ephemeralStorageSize: Size.mebibytes(1024),
          });

Acceptance Criteria

• destinationKeyPrefix is set to match pathPrefix when it's provided
• The existing behavior is unchanged when pathPrefix isn't set
• Testing done

[jjfrench]

Talked with @botanical about this - because the current behavior would've required users to setup redirects, making the default to move the objects when pathPrefix is provided would cause a breaking change for anyone who had setup a redirect. I think we've settled on adding an s3Prefix parameter as a feature rather than the breaking change.