Cannot customize session/artifact/memory services for agents using A2A runner

[calebdelnay]

Describe the bug
The class A2ASendMessageExecutor used by the A2A agent server implementation does not have a constructor that allows injection of various services (session, artifact, memory). This makes it impossible to use any versions of these services that perform persistence. In-memory versions are hard coded.

Additionally, A2ARemoteConfiguration does not look for service beans to pass into A2ASendMessageExecutor.

Expected behavior
Possible to define service implementations that are picked up by the Spring application context and correctly used by A2ARemoteConfiguration and A2ASendMessageExecutor.