fix: Missing an "s" in default_topic_replication

[Sid2728]

Issue description

I had provisioned my redpanda using ansible and set default_topic_replication= 3 for my cluster configurations but on checking it was still 1. After looking around for sometime I found out that the parameter should be default_topic_replications and the docs misses an "s".

Updates to existing documentation

https://docs.redpanda.com/current/reference/properties/cluster-properties/#default_topic_replication

Link to Redpanda Slack conversation

No response

Checks

• New feature
• Content gap
• Support Follow-up
• Small fix (typos, links, copyedits, etc)