docs: document restrictions of colocated tables

Currently some things are not supported for colocated tables: it's not
possible to repair a colocated table, and due to this it's also not
possible to use the tombstone_gc=repair mode on a colocated table.

Extend the documentation to explain what colocated tables are and
document these restrictions.

Fixes scylladb/scylladb#27261

Closes scylladb/scylladb#27516

docs/cql/ddl.rst

@@ -1043,6 +1043,8 @@ The following modes are available:
    * - ``immediate``
      - Tombstone GC is immediately performed. There is no wait time or repair requirement. This mode is useful for a table that uses the TWCS compaction strategy with no user deletes. After data is expired after TTL, ScyllaDB can perform compaction to drop the expired data immediately.
 
+.. warning:: The ``repair`` mode is not supported for :term:`Colocated Tables <Colocated Table>` in this version.
+
 .. _cql-per-table-tablet-options:
 
 Per-table tablet options

docs/operating-scylla/nodetool-commands/cluster/repair.rst

@@ -9,6 +9,8 @@ Running ``cluster repair`` on a **single node** synchronizes all data on all nod
 To synchronize all data in clusters that have both tablets-based and vnodes-based keyspaces, run :doc:`nodetool repair -pr </operating-scylla/nodetool-commands/repair/>` on **all**
 of the nodes in the cluster, and :doc:`nodetool cluster repair </operating-scylla/nodetool-commands/cluster/repair/>` on  **any** of the nodes in the cluster.
 
+.. warning:: :term:`Colocated Tables <Colocated Table>` cannot be synchronized using cluster repair in this version.
+
 To check if a keyspace enables tablets, use:
 
 .. code-block:: cql

docs/reference/glossary.rst

@@ -202,3 +202,7 @@ Glossary
        The name comes from two basic operations, multiply (MU) and rotate (R), used in its inner loop.
        The MurmurHash3 version used in ScyllaDB originated from `Apache Cassandra <https://commons.apache.org/proper/commons-codec/apidocs/org/apache/commons/codec/digest/MurmurHash3.html>`_, and is **not** identical to the `official MurmurHash3 calculation <https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/utils/MurmurHash.java#L31-L33>`_. More `here <https://github.com/russss/murmur3-cassandra>`_.
 
+    Colocated Table
+       An internal table of a special type in a :doc:`tablets </architecture/tablets>` enabled keyspace that is colocated with another base table, meaning it always has the same tablet replicas as the base table.
+       Current types of colocated tables include CDC log tables, local indexes, and materialized views that have the same partition key as their base table.
+