chore: add utility function for retrieving the rules in a bundle [CFG-1291]

[teodora-sandu]

What this does

This functionality was first introduced in #121 but that PR is blocked behind a bug in OPA. This PR extracts the utility function from that PR, which just retrieves the publicIds for all rego rules in a bundle - including duplicates.

Notes for the reviewer

• OPA introduced a new command called inspect which helps us find all the rego rules in a folder: https://github.com/open-policy-agent/opa/blob/main/cmd/inspect.go
• The majority of the code is not exposed in the Golang module so we are adapting a couple lines to read all the rego rules in a folder.
• The inspect command only looks at files and not the contents - but we need a way to get the publicId
• The way we get the publicId is by reading each file and using a regex to extract the publicId which would be configured in a publicId key - the regex allows for any spacing so that no matter what tabbing and newline characters the customer uses, we will retrieve it

More information

• Jira ticket CFG-1291

[teodora-sandu]

@aron This just extracts the utility function from #121, which you already reviewed. It makes most sense for you to look at it but let me know if you'd rather I ask someone else