Allow to specify service level used in select statement `SELECT ... USING SERVICE LEVEL sl_name`.
In OSS, this only affects statement's timeout.
In case both service level and timeout are specified `SELECT ... USING SERVICE LEVEL sl_name AND TIMEOUT 1h`, the timeout has higher priority as statement's timeout.
Fixesscylladb/scylladb#18471Closesscylladb/scylladb#20523
* github.com:scylladb/scylladb:
test/cql-pytest: add test for `SELECT ... USING SERVICE LEVEL`
cql3/Cql.g: extend grammar to allow `SELECT ... USING SERVICE LEVEL`
cql3/statements/select_statement: use service level timeout
cql3/attributes: add service level name field
qos/service_level_controller: add method to check if service level exists in cache
7e7701d436