docs: update doc example for get oauth2-client

[anthonysterling]

👋

This PR updates the example shown by get oauth2-client to show how to extract the client name rather than client secret, as the .client_secret property is never returned by this call which may result in some confusion.

Related issue(s)

Checklist

• I have read the contributing guidelines.
• [] I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  [email protected]) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[CLAassistant]

All committers have signed the CLA.

[alnr]

Thank you!