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FLASHING.md says how to take a newer version of the colleague's tree (copy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/security/r2/SymmetricEncryptionKey.h

@@ -0,0 +1,58 @@
+/*
+ * Generated by asn1c
+ * From ASN.1 module "Ieee1609Dot2BaseTypes"
+ * 	found in "Ieee1609Dot2BaseTypes.asn"
+ * 	`asn1c -fcompound-names -fincludes-quoted -no-gen-example -fprefix=Vanetza_Security2_ -R`
+ */
+
+#ifndef	_Vanetza_Security2_SymmetricEncryptionKey_H_
+#define	_Vanetza_Security2_SymmetricEncryptionKey_H_
+
+
+#include "asn_application.h"
+
+/* Including external dependencies */
+#include "OCTET_STRING.h"
+#include "constr_CHOICE.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Dependencies */
+typedef enum Vanetza_Security2_SymmetricEncryptionKey_PR {
+	Vanetza_Security2_SymmetricEncryptionKey_PR_NOTHING,	/* No components present */
+	Vanetza_Security2_SymmetricEncryptionKey_PR_aes128Ccm,
+	/* Extensions may appear below */
+	Vanetza_Security2_SymmetricEncryptionKey_PR_sm4Ccm
+} Vanetza_Security2_SymmetricEncryptionKey_PR;
+
+/* Vanetza_Security2_SymmetricEncryptionKey */
+typedef struct Vanetza_Security2_SymmetricEncryptionKey {
+	Vanetza_Security2_SymmetricEncryptionKey_PR present;
+	union Vanetza_Security2_SymmetricEncryptionKey_u {
+		OCTET_STRING_t	 aes128Ccm;
+		/*
+		 * This type is extensible,
+		 * possible extensions are below.
+		 */
+		OCTET_STRING_t	 sm4Ccm;
+	} choice;
+	
+	/* Context for parsing across buffer boundaries */
+	asn_struct_ctx_t _asn_ctx;
+} Vanetza_Security2_SymmetricEncryptionKey_t;
+
+/* Implementation */
+extern asn_TYPE_descriptor_t asn_DEF_Vanetza_Security2_SymmetricEncryptionKey;
+extern asn_CHOICE_specifics_t asn_SPC_Vanetza_Security2_SymmetricEncryptionKey_specs_1;
+extern asn_TYPE_member_t asn_MBR_Vanetza_Security2_SymmetricEncryptionKey_1[2];
+extern asn_oer_constraints_t asn_OER_type_Vanetza_Security2_SymmetricEncryptionKey_constr_1;
+extern asn_per_constraints_t asn_PER_type_Vanetza_Security2_SymmetricEncryptionKey_constr_1;
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif	/* _Vanetza_Security2_SymmetricEncryptionKey_H_ */
+#include "asn_internal.h"