Keep the colleague's microbu-esp32c5 tree in this repository

obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).

microbu-esp32c5/external/vanetza-idf/vanetza/asn1/support/der_encoder.h

@@ -0,0 +1,68 @@
+/*-
+ * Copyright (c) 2003-2017 Lev Walkin <vlm@lionet.info>. All rights reserved.
+ * Redistribution and modifications are permitted subject to BSD license.
+ */
+#ifndef	_DER_ENCODER_H_
+#define	_DER_ENCODER_H_
+
+#include "asn_application.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct asn_TYPE_descriptor_s;	/* Forward declaration */
+
+/*
+ * The DER encoder of any type. May be invoked by the application.
+ * Produces DER- and BER-compliant encoding. (DER is a subset of BER).
+ *
+ * NOTE: Use the ber_decode() function (ber_decoder.h) to decode data
+ * produced by der_encode().
+ */
+asn_enc_rval_t der_encode(const struct asn_TYPE_descriptor_s *type_descriptor,
+                          const void *struct_ptr, /* Structure to be encoded */
+                          asn_app_consume_bytes_f *consume_bytes_cb,
+                          void *app_key /* Arbitrary callback argument */
+);
+
+/* A variant of der_encode() which encodes data into the pre-allocated buffer */
+asn_enc_rval_t der_encode_to_buffer(
+    const struct asn_TYPE_descriptor_s *type_descriptor,
+    const void *struct_ptr, /* Structure to be encoded */
+    void *buffer,           /* Pre-allocated buffer */
+    size_t buffer_size      /* Initial buffer size (maximum) */
+);
+
+/*
+ * Type of the generic DER encoder.
+ */
+typedef asn_enc_rval_t(der_type_encoder_f)(
+    const struct asn_TYPE_descriptor_s *type_descriptor,
+    const void *struct_ptr, /* Structure to be encoded */
+    int tag_mode,           /* {-1,0,1}: IMPLICIT, no, EXPLICIT */
+    ber_tlv_tag_t tag, asn_app_consume_bytes_f *consume_bytes_cb, /* Callback */
+    void *app_key /* Arbitrary callback argument */
+);
+
+
+/*******************************
+ * INTERNALLY USEFUL FUNCTIONS *
+ *******************************/
+
+/*
+ * Write out leading TL[v] sequence according to the type definition.
+ */
+ssize_t der_write_tags(const struct asn_TYPE_descriptor_s *type_descriptor,
+                       size_t struct_length,
+                       int tag_mode,      /* {-1,0,1}: IMPLICIT, no, EXPLICIT */
+                       int last_tag_form, /* {0,!0}: prim, constructed */
+                       ber_tlv_tag_t tag,
+                       asn_app_consume_bytes_f *consume_bytes_cb,
+                       void *app_key);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif	/* _DER_ENCODER_H_ */