Fix bucket location patch for the TemplateURL when deploying a stack

[RobertLucian]

Description

When S3 is used as a place of store for the CF artifacts, the resolving of the actual bucketUrl within our patch would lead to the presence of a stringified version of a promise, i.e.: '[object Promise]/cdk/digitalu-local-services/dbdbe3071265081abdd49572f43ec8168bc6fb4250c190631f9e84f51a5ccb4c.yml'. Because of this, what was supposed to be the first prefix within the bucket is now considered to be the bucket. Chaos ensues, and the stack fails to deploy because the S3 bucket "does not exist".

So instead of using promises for our patched version of bucketUrl attribute, we instead determine the bucket name/URL outside of the function associated with it.

While doing this, it was also noticed how the ToolkitInfo object isn't always a ToolkitInfo object anymore:

1. Can be {} (empty key-value pair object).
2. Can be BootstrapStackNotFoundInfo in which case calling bucketUrl or bucketName would throw an exception.
3. Can be ExistingToolkitInfo, which is the ideal case, and also the case when we should patch bucketUrl attribute.

These classes can be observed here: https://github.com/aws/aws-cdk/blob/87e21d625af86873716734dd5568940d41096c45/packages/aws-cdk/lib/api/toolkit-info.ts

[dominikschubert]

Thanks for jumping on this issue.

I'm still not 100% sure for which cases this code path is triggered, as I have not been able to trigger it with a 0815 cdk init ... project & manipulating the stack to be at a size that forces the usage of a TemplateURL parameter when deploying. 🤔

[dominikschubert]

Thanks for jumping on this. I'll have a few more comments that we can iterate over after getting he immediate fix over the line. 🚀