tools: add gen-eventfilter.py

Generate event filtering code for lg2::commit from an input json
file, so that system integrators can create default filtering rules
to omit undesired events and errors from their systems.

Tested:

Used `log-create` to create an event and observed it.  Modified the
default event filter as follows and saw log was not created.

```
@@ -3,6 +3,9 @@
         "default": "allowed"
     },
     "errors": {
-        "default": "allowed"
+        "default": "allowed",
+        "ids": [
+            "xyz.openbmc_project.State.SMC.SMCFailed"
+        ]
     }
 }
```

```
$ ./builddir/log-create xyz.openbmc_project.State.SMC.SMCFailed --json '{ "IDENTIFIER": "/xyz/openbmc_project/inventory/SomeSMC", "FAILURE_TYPE": "Timeout for the SMC" }'
```

Change-Id: Ib6041481075758b994bb27a816dbf5e9f26c2841
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/lib/lg2_commit.cpp b/lib/lg2_commit.cpp
index a35b91e..a2ceb22 100644
--- a/lib/lg2_commit.cpp
+++ b/lib/lg2_commit.cpp
@@ -117,6 +117,16 @@
 auto commit(sdbusplus::exception::generated_event_base&& t)
     -> sdbusplus::message::object_path
 {
+    // Check event filters first.
+    if ((t.severity() == LOG_INFO) && details::filterEvent(t.name()))
+    {
+        return {};
+    }
+    else if (details::filterError(t.name()))
+    {
+        return {};
+    }
+
     if constexpr (LG2_COMMIT_JOURNAL)
     {
         lg2::error("OPENBMC_MESSAGE_ID={DATA}", "DATA", t.to_json().dump());