Update the auto-pulled description string for `changefeed.balance_range_distribution.enable` cluster setting

[katmayb]

Recently received the following docs issue regarding updating the description for the changefeed.balance_range_distribution.enable cluster setting on this page: https://www.cockroachlabs.com/docs/stable/cluster-settings.html.

Descriptions on this page are automatically pulled from strings in the cockroach repo. This will need to be changed there in order to update this description. See @data-matt's docs issue for more detail: https://cockroachlabs.atlassian.net/browse/DOC-7398

Jira issue: CRDB-26869

[blathers-crl]

cc @cockroachdb/cdc

[amruss]

We should also enable this to true by default