Introduce new database config option `schema_registry_grace_period`
describing the amount of time in seconds after which unused schema
versions will be cleaned up from the schema registry cache.
Default value is 1 second, the same value as was hardcoded before.
Tests: unit(debug)
Refs: #7225
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Message-Id: <20200915131957.446455-1-pa.solodovnikov@scylladb.com>