Update add-hashicorp-vault.md

[lorenyeung]

trafficstars

correct sub field for jwt auth in vault connector when FF is enabled

Thanks for contributing to the Harness Developer Hub! Our code owners will review your submission.

Description

• Please describe your changes: update sub field documentation for jwt auth in vault connector to have different scope requirements
• Jira/GitHub Issue numbers (if any): ______________________________
• Preview links/images (Internal contributors only): __________________

PR lifecycle

We aim to merge PRs within one week or less, but delays happen sometimes.

If your PR is open longer than two weeks without any human activity, please tag a code owner in a comment.

PRs must meet these requirements to be merged:

• [ ] Successful preview build.
• [ ] Code owner review.
• [ ] No merge conflicts.
• [ ] Release notes/new features docs: Feature/version released to at least one prod environment.

[bot-gitexp-user]

Please check the Execution Link of the Pipeline for the Website Draft URL. This is located in the Preview Step behind the Harness VPN and also is available in #hdh_alerts. E.g Website Draft URL: https://unique-id--harness-developer.netlify.app. Current Draft URL is: https://680b19606d9ae958075b4f45--harness-developer.netlify.app