Localize flags to each subcommand

[nsmith5]

Summary

Makes CLI usage a little more clear by moving global flags to their relevant subcommands.

Before

$ fulcio createca -h
Create an x509 root CA within a pkcs11 device using values
such as organization, country etc. This can then be used as the root
certificate authority for an instance of sigstore fulcio

Usage:
  fulcio createca [flags]

Flags:
      --country string          Country name for root CA
  -h, --help                    help for createca
      --hsm string              The HSM provider to use. Valid values: softhsm (default), aws (default "softhsm")
      --locality string         Locality name for root CA
      --org string              Organization name for root CA (default "Fulcio Root CA")
      --out string              output root CA to file
      --postal-code string      Postal code for root CA
      --province string         Province name for root CA
      --street-address string   Street address for root CA

Global Flags:
      --aws-hsm-root-ca-path string     Path to root CA on disk (only used with AWS HSM)
      --ca string                       googleca | pkcs11ca | ephemeralca (for testing)
      --config-path string              path to fulcio config json (default "/etc/fulcio-config/config.json")
      --ct-log-url string               host and path (with log prefix at the end) to the ct log (default "http://localhost:6962/test")
      --gcp_private_ca_parent string    private ca parent: /projects/<project>/locations/<location>/<name> (only used with --ca googleca)
      --gcp_private_ca_version string   private ca version: [v1|v1beta1] (only used with --ca googleca) (default "v1")
      --host string                     The host on which to serve requests (default "0.0.0.0")
      --hsm-caroot-id string            HSM ID for Root CA (only used with --ca pkcs11ca)
      --log_type string                 logger type to use (dev/prod) (default "dev")
      --pkcs11-config-path string       path to fulcio pkcs11 config file (default "config/crypto11.conf")
      --port string                     The port on which to serve requests (default "8080")

NB: The flags like --port that are completely irrelevant to createca and are only needed for serve

After

fulcio createca -h
Create an x509 root CA within a pkcs11 device using values
such as organization, country etc. This can then be used as the root
certificate authority for an instance of sigstore fulcio

Usage:
  fulcio createca [flags]

Flags:
      --country string              Country name for root CA
  -h, --help                        help for createca
      --hsm string                  The HSM provider to use. Valid values: softhsm (default), aws (default "softhsm")
      --hsm-caroot-id string        HSM ID for Root CA
      --locality string             Locality name for root CA
      --org string                  Organization name for root CA (default "Fulcio Root CA")
      --out string                  output root CA to file
      --pkcs11-config-path string   path to fulcio pkcs11 config file (default "config/crypto11.conf")
      --postal-code string          Postal code for root CA
      --province string             Province name for root CA
      --street-address string       Street address for root CA

Ticket Link

Fixes #273

Release Note

* Removed global flags from CLI and moved flags to their relevant subcommands

[dlorenc]

Thanks for the contributions!