rpc: implement the ADR 075 /events method (#7965)

This method implements the eventlog extension interface to expose ABCI metadata
to the log for query processing. Only the types that have ABCI events need to
implement this.

- Add an event log to the environment
- Add a sketch of the handler method
- Add an /events RPCFunc to the route map
- Implement query logic
- Subscribe to pubsub if confingured, handle termination

light/proxy/routes.go

@@ -2,7 +2,10 @@ package proxy
 
 import (
 	"context"
+	"errors"
+	"time"
 
+	"github.com/tendermint/tendermint/internal/eventlog/cursor"
 	tmbytes "github.com/tendermint/tendermint/libs/bytes"
 	lrpc "github.com/tendermint/tendermint/light/rpc"
 	rpcclient "github.com/tendermint/tendermint/rpc/client"
@@ -27,6 +30,17 @@ func (p proxyService) GetConsensusState(ctx context.Context) (*coretypes.ResultC
 	return p.ConsensusState(ctx)
 }
 
+// TODO(creachadair): Remove this once the RPC clients support the new method.
+// This is just a placeholder to let things build during development.
+func (proxyService) Events(ctx context.Context,
+	filter *coretypes.EventFilter,
+	maxItems int,
+	before, after cursor.Cursor,
+	waitTime time.Duration,
+) (*coretypes.ResultEvents, error) {
+	return nil, errors.New("the /events method is not implemented")
+}
+
 func (p proxyService) Subscribe(ctx context.Context, query string) (*coretypes.ResultSubscribe, error) {
 	return p.SubscribeWS(ctx, query)
 }