--idp-jwt warning for flag that doesn't exist

[hawksight]

PROBLEM SUMMARY

vcert getcred -p vcp --token-url https://api.venafi.cloud/v1/oauth2/v2.0/XXXXXX/token --verbose

vCert: 2024/07/22 17:06:00 missing jwt for service account authentication. Set the jwt using --idp-jwt flag

STEPS TO REPRODUCE

See above ^.
Use the getcred subcommand without providing a JWT option, but do include token-url.

EXPECTED RESULTS

Waning should say:

vCert: 2024/07/22 17:06:00 missing jwt for service account authentication. Set the jwt using --external-jwt flag
``

**ACTUAL RESULTS**
<!-- explain what actually happened when you performed the repro steps; exact error messages and screenshots, if applicable -->

Referes to `--idp-jwt` flag which does not exist.

**ENVIRONMENT DETAILS**
<!-- tell us which version you are using for this solution and any other products involved (Venafi or other) -->

```log
vcert version v5.7.1

MacOSX.

COMMENTS/WORKAROUNDS

Use the correct flag. This is more of documentation / logging issue.