Description of problem:
the error message "opm index prune" a file-based index image is not clear, the message "Error: index image xxxx missing label operators.operatorframework.io.index.database.v1" is confusing.

Version-Release number of selected component (if applicable):
[root@preserve-olm-agent-test ~]# opm version
Version: version.Version{OpmVersion:"13f7723ba", GitCommit:"13f7723ba6098a17c7c44da17d844bb0d87d30a7", BuildDate:"2021-12-29T01:32:43Z", GoOs:"linux", GoArch:"amd64"}

How reproducible:
always

Steps to Reproduce:
[root@preserve-olm-agent-test ~]# opm alpha list packages quay.io/olmqe/etcd-index:47322-single
NAME            DISPLAY NAME   DEFAULT CHANNEL
ditto-operator  Eclipse Ditto  v2.0
etcd            etcd           alpha-1

1.opm index prune -p etcd --from-index quay.io/olmqe/etcd-index:47322-single
WARN[0000] DEPRECATION NOTICE:
Sqlite-based catalogs and their related subcommands are deprecated. Support for
them will be removed in a future release. Please migrate your catalog workflows
to the new file-based catalog format. 
INFO[0000] pruning the index                             packages="[etcd]"
INFO[0000] Pulling previous image quay.io/olmqe/etcd-index:47322-single to get metadata  packages="[etcd]"
INFO[0000] running /usr/bin/podman pull quay.io/olmqe/etcd-index:47322-single  packages="[etcd]"
INFO[0001] running /usr/bin/podman pull quay.io/olmqe/etcd-index:47322-single  packages="[etcd]"
INFO[0002] Getting label data from previous image        packages="[etcd]"
INFO[0002] running podman inspect                        packages="[etcd]"
Error: index image quay.io/olmqe/etcd-index:47322-single missing label operators.operatorframework.io.index.database.v1
Usage:
  opm index prune [flags]

Flags:
  -i, --binary-image opm        container image for on-image opm command
  -c, --container-tool string   tool to interact with container images (save, build, etc.). One of: [docker, podman] (default "podman")
  -f, --from-index string       index to prune
      --generate                if enabled, just creates the dockerfile and saves it to local disk
  -h, --help                    help for prune
  -d, --out-dockerfile string   if generating the dockerfile, this flag is used to (optionally) specify a dockerfile name
  -p, --packages strings        comma separated list of packages to keep
      --permissive              allow registry load errors
  -t, --tag string              custom tag for container image being built

Global Flags:
      --skip-tls   skip TLS certificate verification for container image registries while pulling bundles or index

2.
3.

Actual results:
the error message is not clear.
"Error: index image quay.io/olmqe/etcd-index:47322-single missing label operators.operatorframework.io.index.database.v1"

Expected results:

the error message should be more clear, for example "opm index prune doesn’t support file-based catalog" or "opm index prune only support sqlite-based catalog"

Additional info: