[filebeatreceiver] support log input

[leehinman]

When running as filebeatreceiver we need the log input to be available since many integrations still require it.

beats/filebeat/input/log/input.go

Lines 88 to 90 in 370ec85

	func AllowDeprecatedUse(cfg *conf.C) bool {
	allow, _ := cfg.Bool(allowDeprecatedUseField, -1)
	return allow || fleetmode.Enabled() || fileset.CheckIfModuleInput(cfg)

currently disables the log input under filebeatreceiver because fleetmode is not enabled. We don't want to enable fleet mode because that will break other things.

The simplest fix is probably to inject allow_deprecated_use into the config before it is passed to NewInput. When we have a beats receiver manager we could have a better check.

We can't just enable fleet mode. That would change behavior to expect grpc control socket. A full fix should also take into account #44604

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)