CAMEL-23614: Add getFromRouteGroup() to Exchange API

[davsclaus]

Summary

• Adds getFromRouteGroup() method to the Exchange interface, allowing users to retrieve the route group of the originating route
• Implementation in AbstractExchange resolves the group via getFromRouteId() → getContext().getRoute(id).getGroup() with null-safe checks
• Includes unit test SedaFromRouteGroupTest verifying group is propagated and null when not set

Test plan

• SedaFromRouteGroupTest passes — verifies getFromRouteGroup() returns "myGroup" for grouped route and null for ungrouped route
• CI green

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