RS: Fixed authenticate DB connections with cert-based auth

[rrelledge]

Note

Low Risk
Low risk documentation-only change; it only updates wording/formatting and does not affect runtime behavior.

Overview
Updates the certificate-based authentication docs to clarify that database connections require a client cert that is either explicitly added to the DB for mTLS (via authentication_ssl_client_certs) or signed by a trusted CA, rather than implying only the cluster mtls_trusted_ca is valid.

Applies the same clarification to the 7.8, 7.22, and unversioned pages, and fixes minor formatting (restores the Limitations bullet/newline).

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[github-actions]

DOC-6490

[github-actions]

Staging links:
https://redis.io/docs/staging/DOC-6490/operate/rs/7.22/security/certificates/certificate-based-authentication/
https://redis.io/docs/staging/DOC-6490/operate/rs/7.8/security/certificates/certificate-based-authentication/
https://redis.io/docs/staging/DOC-6490/operate/rs/security/certificates/certificate-based-authentication/

[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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^{Security scan by Jit}