(DOCSP-7885): x509 c snippet (#587)

* (DOCSP-7885): added C connection code

* added count_document to c example

* added collection.destroy to prevent leak on clang x509 snip

* (DOCSP-7885): updated c snippet to address comments

* updated c code with proper formatting using clang-format -style=file -i

* update error and move variable declorations to top

Author: Mohammad Hunan Chughtai

source/includes/connection-snippets/x509-snippets/c-connection.c

@@ -0,0 +1,36 @@
+// begin x509 connection
+#include <mongoc/mongoc.h>
+#include <stdio.h>
+
+int main(int argc, char *argv[]) {
+  mongoc_collection_t *collection;
+  mongoc_client_t *client;
+  int64_t count;
+  bson_t filter;
+  bson_error_t error;
+
+  mongoc_init();
+
+  client = mongoc_client_new(
+      "mongodb+srv://<cluster-url>/"
+      "test?authSource=$external&tlsCertificateKeyFile=/etc/certs/mongodb/"
+      "client.pem&retryWrites=true&w=majority&authMechanism=MONGODB-X509");
+
+  collection = mongoc_client_get_collection(client, "testDB", "testCol");
+  filter = BSON_INITIALIZER;
+  count = mongoc_collection_count_documents(collection, &filter, NULL, NULL,
+                                            NULL, &error);
+
+  if (count < 0) {
+    fprintf(stderr, "Count failed: %s\n", error.message);
+  } else {
+    printf("%" PRId64 " documents counted.\n", count);
+  }
+  bson_destroy(&filter);
+  mongoc_collection_destroy(collection);
+  mongoc_client_destroy(client);
+  mongoc_cleanup();
+
+  return 0;
+}
+// end x509 connection