plugin_proxy: enable event_type specification for proxy plugins

This commit adds event_type to the flb_plugin_proxy_def struct. This allows for the setting
of event_type to a value other than the default log only initialization.

In the flb_plugin_proxy_register function default behaviour is enforced by checking for unset event_type vlaues.
When unset (a value of 0) then log behaviour is defaulted. No need for incorrect value checking since this
was not a set field in the past. Unset fields are set as current behavior dicates and future usecases using incorrect values can be treated as user error.

Input use case does not use event-type and is unaffected by this change.

Signed-off-by: jmccormick7 <jcm258@case.edu>

Author: jmccormick7

include/fluent-bit/flb_plugin_proxy.h

@@ -40,6 +40,7 @@ struct flb_plugin_proxy_def {
     int flags;
     char *name;               /* plugin short name                           */
     char *description;        /* plugin description                          */
+    int event_type;           /* event type (logs/metrics/traces)            */
 };
 
 /* Proxy context */

src/flb_plugin_proxy.c

@@ -362,6 +362,14 @@ static int flb_proxy_register_output(struct flb_plugin_proxy *proxy,
     out->flags = def->flags;
     out->name  = flb_strdup(def->name);
 
+    /* If event_type is unset (0) then default to logs (this is the current behavior) */
+    if (def->event_type == 0) {
+        out->event_type = FLB_OUTPUT_LOGS;
+    }
+    else {
+        out->event_type = def->event_type;
+    }
+
     out->description = def->description;
     mk_list_add(&out->_head, &config->out_plugins);
 
@@ -396,6 +404,7 @@ static int flb_proxy_register_input(struct flb_plugin_proxy *proxy,
     in->flags = def->flags | FLB_INPUT_THREADED;
     in->name  = flb_strdup(def->name);
     in->description = def->description;
+
     mk_list_add(&in->_head, &config->in_plugins);
 
     /*