fix(response_cache): don't duplicate redis connection if we specify custom config for a subgraph

[bnjjj]

Response Cache - Redis Connection Management

Fixed an issue where the response cache would create duplicate Redis connections when a custom configuration was specified for individual subgraphs (without any specific Redis configuration). Previously, if a subgraph inherited the same Redis configuration from the global all setting, the router would unnecessarily establish a redundant connection. Now, the router correctly reuses the existing connection pool when the configuration is identical, improving resource efficiency and reducing connection overhead.

Impact: Users with response caching enabled who specify Redis configurations at both the global and subgraph levels will see reduced Redis connection usage, leading to better resource utilization.

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[apollo-librarian]

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Build ID: e84f01f93b992ac40be84283
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[carodewig]

Just a few minor comments - overall looks great!

[bnjjj]

Updated @carodewig ! Thanks for the review