Extend the cql3 truncate statement to accept attributes,
similar to modification statements.
To achieve that we define cql3::statements::raw::truncate_statement
derived from raw::cf_statement, and implement its pure virtual
prepare() method to make a prepared truncate_statement.
The latter is no longer derived from raw::cf_statement,
and just stores a schema_ptr to get to the keyspace and column_family.
`test_truncate_using_timeout` cql-pytest was added to test
the new USING TIMEOUT feature.
Fixes#11408
Also, update docs/cql/ddl.rst truncate-statement section respectively.
Closes#11409
* github.com:scylladb/scylladb:
docs: cql-extensions: add TRUNCATE to USING TIMEOUT section.
docs: cql: ddl: add support for TRUNCATE USING TIMEOUT
cql3, storage_proxy: add support for TRUNCATE USING TIMEOUT
cql3: selectStatement: restrict to USING TIMEOUT in grammar
cql3: deleteStatement: restrict to USING TIMEOUT|TIMESTAMP in grammar
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