Add ability to pass glob patterns to match image, and add "exempt" policy

[codysoyland]

This PR adds Helm values policy.images and policy.exemptImages to the trust-policies Helm chart. policy.images is a list of image glob patterns that the policy applies to, and policy.exemptImages is a list of image glob patterns that will be exempt from verification.

Usage:

helm install trust-policies \
--atomic \
--namespace artifact-attestations \
--version v0.5.0 \
--set policy.enabled=true \
--set policy.images[0]='ghcr.io/my-org/**' \
--set policy.exemptImages[0]="index.docker.io/library/busybox**" \
oci://ghcr.io/github/artifact-attestations-helm-charts/trust-policies

[bdehamer]