Rename is_replication_enabled to enable_replication (#676)

<!-- Describe what has changed in this PR -->
**What changed?**
Renaming field to be consistent with enable_remote_cluster_connection
from temporalio/api#672

<!-- Tell your future self why have you made these changes -->
**Why?**
CLI experience/readability headache to have inconsistency

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**Breaking changes**
should be ok, field is new and unused

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right after this PR was merged. -->
**Server PR**
na

Author: michaely520