feat: allow multi region stackset deployments with file assets

[josh-demuth]

Fixes #159

Added support to use file assets across multiple regions in one stackset. This still requires to pass the asset bucket(s) to the construct. It also uses a bucket "prefix" which the stackset construct will append "-${region}" to the end of the bucket name. For example, all asset buckets across each region will need to have the same prefix like "assetbucket" and will need the region appended at the end "assetbucket-us-east-1" "assetbucket-us-west-2". it is out of scope of the construct to create these buckets at this time.

[madeline-k]

• update projenrc
• update example - prefix should not have a region at the end

[gshpychka]

Worth calling out that you are only talking about file assets when you say "assets". i.e. Docker image assets are not supported

[josh-demuth]

Worth calling out that you are only talking about file assets when you say "assets". i.e. Docker image assets are not supported

good point. unfortunately docker assets would need a stable upstream construct similar to https://github.com/cdklabs/cdk-ecr-deployment. it is out of scope of this construct to build this at this time. similar to how the Service Catalog L2 does not support docker assets at this time.

[jwestbrook]

Of note this merge breaks the previous bucket asset setup. If you have an asset bucket that does not have a region name in the bucket name, you need to deprecate that bucket, and add a new bucket that contains the region in the name.

For anyone else, note assetBucketPrefix does not refer to the traditional AWS S3 object prefixes, it's referring to the bucket name only. The Readme uses the string 'prefix' which is a little vague. So as an example, if you pass the string 'my-org-stackset-assets' to assetBucketPrefix then you should have a bucket named my-org-stackset-assets-us-east-1 for any stacksets that deploy to us-east-1, and a bucket named my-org-stackset-assets-us-west-2 for any stacksets that deploy to us-west-2, etc.

IMO, a sanity check against the array of IBucket objects to check the bucket name ends with any region value string or the specific region value string this stackset is deploying to would be helpful.