CASSANDRA-21218: Fix typos in documentation

[Shanzita]

Fix typos in documentation

Fixed the following typos in the documentation:

• repair.adoc (line 3): "it's nodes" → "its nodes"
• repair.adoc (line 107): "Similiar" → "Similar"
• ddl.adoc (line 36): "If is is not" → "If it is not"
• data-modeling_refining.adoc (line 26): "number of of values" → "number of values"
• accord-architecture.adoc (line 248): "by the the whole cluster" → "by the whole cluster"

patch by Shanzitaa; reviewed by TBD for CASSANDRA-21218