Enhance get_digest.sh script

[gianlucam76]

Currently get_digest.sh only gets digests for Sveltos images given a tag.

A nice enhancement would be for it to automatically update values.yaml

For every Sveltos components there is a section like this

    image:
      repository: docker.io/projectsveltos/access-manager
      tag: v0.46.1
      digest: sha256:c7794284849869f58c8bbb4df0effa89b7a7ede4944ee13b59dcd1693f19b168

it would be nice to extend get_digest.sh to get digest, and then update this section. For instance lets say we run

./get_digest.sh v0.47.0

starting from

    image:
      repository: docker.io/projectsveltos/access-manager
      tag: v0.46.1
      digest: sha256:c7794284849869f58c8bbb4df0effa89b7a7ede4944ee13b59dcd1693f19b168

after getting the digest for access-manager v0.47.0 this could be

    image:
      repository: docker.io/projectsveltos/access-manager
      tag: v0.47.0
      digest: sha256:xxxxxxxxxxxxxxxx