Do not update keeper replica count

[MaxVanDijck]

reading the helm chart values there is this comment # !! DO NOT CHANGE AFTER INITIAL DEPLOYMENT:
https://github.com/Altinity/helm-charts/blame/13b84720f0f6c728d270e737b7f9a14fc476c6d5/charts/clickhouse/values.yaml#L203

but following the git blame + pull-request does not provide sufficient context for:

1. Why we should not change the ch-keeper replication count and context behind this comment
2. How we can actually change the replication count after deployment

Could this be updated to provide sufficient context i.e by linking to the altinity knowledge base or other documentation?