Fix incorrect rladmin command in create-certificates.md (fixes #3737)

[harshh6305]

Fixes #3737

Problem

The "Install certificates" section instructed users to check certificate status using:

   rladmin status certificates

This command doesn't work — rladmin has no certificates subcommand, resulting in:

   ERROR: invalid token 'certificates'

Fix

Replaced the incorrect command with an openssl x509 command to verify the installed certificate's expiration dates, as suggested in the issue.

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Note

Low Risk
Documentation-only change with no runtime or security impact.

Overview
Fixes the Install certificates verification step in create-certificates.md by replacing the non-existent rladmin status certificates command (which errors with invalid token 'certificates') with openssl x509 -in /path/to/redis-cert-chain.pem -noout -dates so readers can confirm the installed cert’s validity dates after upload.

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