[VC-43403] Add Local File output path mode

[wallrj-cyberark]

Changes:

• Refactored TLSPKMode to a more general OutputMode.
• Added a new Local File output mode.

Next I'd like to add a MachineHub mode:

• [VC-43403] CyberArk(agent): add support for MachineHub output mode #696

Later I'll try and figure how we can allow multiple output modes.

Testing

$ go run . agent    --agent-config-file examples/one-shot-secret.yaml    --one-shot    --output-path output.json
I0822 12:06:42.354685  284845 run.go:58] "Starting" logger="Run" version="development" commit=""
I0822 12:06:42.355219  284845 run.go:116] "Healthz endpoints enabled" logger="Run.APIServer" addr=":8081" path="/healthz"
I0822 12:06:42.355273  284845 run.go:120] "Readyz endpoints enabled" logger="Run.APIServer" addr=":8081" path="/readyz"
I0822 12:06:42.355300  284845 run.go:269] "Pod event recorder disabled" logger="Run" reason="The agent does not appear to be running in a Kubernetes cluster." detail="When running in a Kubernetes cluster the following environment variables must be set: POD_NAME, POD_NODE, POD_UID, POD_NAMESPACE"
I0822 12:06:42.558945  284845 client_file.go:35] "Data saved to local file" logger="Run.gatherAndOutputData.postData" outputPath="output.json"
I0822 12:06:42.558992  284845 run.go:417] "Data sent successfully" logger="Run.gatherAndOutputData.postData"

$ jq  -r '.[] | .data.items[] | .resource.metadata | "\(.namespace)/\(.name)"' < output.json
gmp-system/collection
gmp-system/rules
gmp-system/webhook-tls
team-1/app-0
venafi/cert-manager-approver-policy-tls
venafi/cert-manager-webhook-ca
default/venafi-kubernetes-agent-e2e.a2074131-f85a-48c0-88be-fb1a1d871a3b
gmp-system/alertmanager