Add Redis Search module support

[imperugo]

Summary

Add support for Redis Search (RediSearch) for full-text search, secondary indexing, and aggregation.

Key Operations

• `FT.CREATE` — create search index
• `FT.SEARCH` — full-text search
• `FT.AGGREGATE` — aggregation queries
• `FT.DROPINDEX` — drop index

Considerations

• Requires Redis Stack
• SE.Redis may not have native API — may need raw `ExecuteAsync`
• Consider NRedisStack library integration
• Separate package: `StackExchange.Redis.Extensions.Search`
• Lower priority than VectorSet and JSON since it's more niche