using codebuild as deploy paired with ou path gives unclear error

```
default_providers:
source:
provider: codecommit
properties:
account_id: "123456789012"
deploy:
provider: codebuild
properties:
image: AMAZON_LINUX_2
spec_filename: deployspec.yml`
targets:
- /ou/test/123 <-- expecting account id
```

Results in an error about construct names for the stage already existing as it attempts to create multiple codebuild stages with the same name. This works as intended when using account ids as opposed to OU paths as it then only targets a single account and thus there is no duplicate stage name attempts.

The question becomes what would we like this to do when using a path? an idea could be that it fetches the account ids from the ou path and inserts them as an environment variable into a single codebuild project (stage).

Start by reproducing the default_providers deploy configuration with provider codebuild and the /ou/test/123 target, then trace how OU paths expand into deployment stages. Compare that flow with account-ID targets and establish the intended behavior for a path target. Done means the configuration no longer produces duplicate stage names and the resulting behavior is documented or covered by a regression test.

Written by the indexing model from the issue text.