Key prefixing is not handled properly in IndexSchema

[tylerhutcherson]

langchain-redis/libs/redis/langchain_redis/vectorstores.py

Line 354 in 0e6c3c1

"prefix": f"{self.config.key_prefix}:",

This adds an additional : which creates an "empty" section of the key. Need to handle this and also figure out how to enable proper migration when released. This might break some implementations. But need to see the extent of the impact.