bug(cloudrun): fix parseContainerImage to handle images with registry…

[zyzzmohit]

What this PR does:
This PR addresses a parsing issue within pkg/app/piped/platformprovider/cloudrun/servicemanifest.go. The previous implementation of parseContainerImage naively split the image URI by : to find the tag, which broke when a service manifest utilized an image from a custom Docker registry containing a port (e.g., localhost:5000/image:tag).

The new implementation isolates the last segment of the URI path and correctly searches for the tag's delimiter strictly using strings.LastIndex.

I have also added multiple dedicated unit test cases in servicemanifest_test.go for both FindImageTag and FindArtifactVersions to guarantee this behavior.

Why we need it:
Cloud Run services referencing images using custom registry ports will now correctly deploy without parsing errors during the repository artifact retrieval phase.

Which issue(s) this PR fixes:
Fixes #6571

Does this PR introduce a user-facing change?:

• How are users affected by this change: No direct UX changes. Users deploying Cloud Run applications from private registries with custom ports will no longer experience failed deployments.
• Is this breaking change: No.
• How to migrate (if breaking change): N/A