digesta-bot: Support Helm Chart (separate image and tag fields)

[faisal-memon]

Lots of helm charts have image: and tag: on separate lines. For example from SPIRE helm chart:

    registry: cgr.dev
    # -- The repository within the registry
    repository: chainguard/bash
    # -- Overrides the image tag
    tag: latest@....

Would be great if digesta bot handled this layout.