fix(vault): use vault-secrets-provider's "latest" image tag

mentioned in commit c50a3a4e

mentioned in merge request to-be-continuous/samples/python-serverless-on-aws!135 (merged)

mentioned in merge request to-be-continuous/samples/cloudformation-on-aws!19 (merged)

mentioned in merge request to-be-continuous/samples/golang-docker-on-aws!112 (merged)

mentioned in merge request to-be-continuous/samples/cloudformation-on-aws!22 (merged)