fix LocalStack legacy mode detection for "latest" tag variations

[alexrashed]

Motivation

While looking into #7390 and digging into the legacy mode check for LocalStack I stumbled upon an issue when using specific latest images, like:

• localstack/localstack:s3-latest (a minimal image which basically only contains S3)
• localstack/localstack-pro:latest-bigdata (a LocalStack Pro image which contains disk-space heavy packages which would otherwise be downloaded on demand)

If this is the case, the default fallback currently is to jump back to useLegacyMode=true which is not compatible with up-to-date images.
In the long run, I would propose to change the default fallback (as mentioned in #7390 (comment)), but this PR aims at fixing the issue for these specific tags for now.

Changes

• Extends the "latest check" such that multiple variations of the "latest" tags are possible (see above).
• Adds a unit test which tests various version strings with the shouldRunInLegacyMode action (and makes the function package private to allow directly testing it).

[eddumelendez]

Thanks for your contribution, @alexrashed !