⭐️ Allow loading policies from an s3 bucket.

[preslavgerchev]

Introduce a BundleResolver interface and 2 concrete implementations:

• A local (file) resolver
• An s3 resolver

The BundleFromPaths will iterate through the possible resolvers and find the right one for the target we're specifying

This allows for pulling policies from an s3 bucket:

~/go/bin/cnspec scan -f s3://mysupernotexistingbucket1234567

Or local (like before, unchanged)

~/go/bin/cnspec scan -f packs.yaml

It also supports pulling a specific s3 item:

~/go/bin/cnspec scan -f s3://mysupernotexistingbucket1234567/packs.mql.yaml

It also works with both at the same time:

// s3 bucket + local
~/go/bin/cnspec scan -f s3://mysupernotexistingbucket1234567 -f packs.yaml

// s3 key + local
~/go/bin/cnspec scan -f s3://mysupernotexistingbucket1234567/pol.mql.yaml -f packs.yaml

[chris-rock]

Thank you @preslavgerchev Great work.

Can you please fix the nits and add some tests for the bundle resolver?