Load Bedrock identity verifier metadata

[robinbraemer]

Summary

• load Bedrock identity verifier keys from signed-key metadata with cache and static fallback
• accept current and previous verifier public keys during rotation
• carry endpoint and organization scope from p2p/session proposals into Bedrock identity enforcement
• expose connector config for public-keys, metadata-url, and metadata-cache-seconds

Verification

• ./gradlew :core:test --tests com.minekube.connect.watch.SessionProposalTest --tests com.minekube.connect.tunnel.p2p.Libp2pSessionMapperTest --tests com.minekube.connect.tunnel.p2p.Libp2pSessionResponderTest --no-daemon
• ./gradlew :core:test --tests com.minekube.connect.config.ConfigLoaderTest --tests com.minekube.connect.bedrock.BedrockIdentityKeyProviderTest --no-daemon
• ./gradlew :core:test --tests com.minekube.connect.bedrock.BedrockIdentityEnforcerTest --no-daemon
• ./gradlew build --no-daemon
• git diff --check

Tracks private rollout issues GeyserMC#423 and GeyserMC#425.