Add CloudConfigStore protobuf service

[VinceBT]

JavaSteam ships the Steam Cloud (file storage) messages but not CloudConfigStore, which is the namespace where things like user-defined game collections live. Without it there's no way to call CloudConfigStore.Download from a UnifiedMessages handler, so I had to hand-roll the protobuf + a service stub downstream.

This adds steammessages_cloudconfigstore.steamclient.proto (messages + the CloudConfigStore / CloudConfigStoreClient services), mirroring the sibling steammessages_cloud.steamclient.proto layout. The message definitions come straight from SteamDB's Protobufs.

The RPC generator picks it up automatically (no extra wiring needed):

[steammessages_cloudconfigstore.steamclient.proto] - found "CloudConfigStore", which has 2 methods
[steammessages_cloudconfigstore.steamclient.proto] - found "CloudConfigStoreClient", which has 1 methods

generateProto + generateRpcMethods build clean and produce SteammessagesCloudconfigstoreSteamclient plus the CloudConfigStore service stub.

[LossyDragon]

This looks to be a webui protobuf? If so, put it here src/main/proto/in/dragonbra/javasteam/protobufs/webui.

Reference: https://github.com/SteamTracking/Protobufs/blob/master/webui/service_cloudconfigstore.proto

[VinceBT]

Good call, moved it to protobufs/webui/service_cloudconfigstore.proto with the webui java_package. Only tweak vs the clientcomm one: CloudConfigStoreClient.NotifyChange returns .NoResponse, which is only defined in steammessages_unified_base, so I import that. generateProto + generateRpcMethods build clean and the service stub still gets picked up.

[LossyDragon]

Looks good, thanks! That NoResponse should be fine to use. The WebUI protos are pretty new for JavaSteam and I recall protobufs are picky if there are two signatures with the same name in the .proto. package. That's rainy day project to port common_base to webui for consistency.