182: Removing unwanted default value for list option to safe command

[abhishek44sharma]

Removing unwanted default value for list option to safe command.
Sample help output for safe command:
k exec -it -n vsecm-system vsecm-sentinel-787bb957c6-mpxw5 -- safe -h

usage: safe [-h|--help] [-l|--list] [-k|--use-k8s] [-d|--delete] [-a|--append]
[-n|--namespace ""] [-i|--input-keys ""] [-b|--store
""] [-w|--workload ""] [-s|--secret ""]
[-t|--template ""] [-f|--format ""] [-e|--encrypt]

Assigns secrets to workloads.

Arguments:

-h --help Print help information
-l --list lists all registered workloads.
-k --use-k8s update an associated Kubernetes secret upon save. Overrides
VSECM_SAFE_USE_KUBERNETES_SECRETS.. Default: false
-d --delete delete the secret associated with the workload.. Default:
false
-a --append append the secret to the existing secret collection
associated with the workload.. Default: false
-n --namespace the namespace of the Kubernetes Secret to create.. Default:
default
-i --input-keys A string containing the private and public Age keys and AES
seed, each separated by '\n'.
-b --store backing store type (file|memory) (default: file). Overrides
VSECM_SAFE_BACKING_STORE.
-w --workload name of the workload (i.e. the '$name' segment of its
ClusterSPIFFEID
('spiffe://trustDomain/workload/$name/…')).
-s --secret the secret to store for the workload.
-t --template the template used to transform the secret stored.
-f --format the format to display the secrets in. Has effect only when
-t is provided. Valid values: yaml, json, and none.
Defaults to none.
-e --encrypt returns an encrypted version of the secret if used with
-s; decrypts the secret before registering it to the
workload if used with -s and -w.. Default: false

[v0lkan]

LGTM.