Fixes #7481

Motivation
Default bookkeeper conf that ships with apache pulsar indicates that the unit of openLedgerRereplicationGracePeriod is in seconds, but official bookkeeper doc(and code) mentions that the unit is in milliseconds.

Pulsar should configure default as 30000 instead of 30 and bookkeeper.conf should mention that the unit of this period is milliseconds instead of seconds.

Modifications
Update the bookkeep.config file
Update the following Pulsar docs for releases 2.5.2, 2.6.0, 2.6.1, and master
Reference > Pulsar Config > BookKeeper