release-23.2: roachtest/cdc: ensure hydra endpoint is up

[rharding6373]

Backport 1/1 commits from #123345.

/cc @cockroachdb/release

---

When we start hydra to enable oauth during roachtest testing, the admin endpoint may not have started before the create oauth client command is called, resulting in a test failure. This PR puts the create command in a retry loop with a timeout so that the command has a chance to succeed.

Fixes: #122456
Epic: None

Release note: None

Release Justification: Test-only change to deflake CDC roachtests by waiting until hydra endpoint is up to start oauth.

[blathers-crl]

Thanks for opening a backport.

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[cockroach-teamcity]

This change is 

[renatolabs]

Thanks for backporting!