Add sbom descripton file for Software BOM

This file is used by the esp-idf-sbom tool to generate
an SBOM file in the SPDX format for esp-idf projects.

sbom.yml

@@ -0,0 +1,11 @@
+name: 'lwip'
+version: '2.1.2'
+cpe: cpe:2.3:a:lwip_project:lwip:{}:*:*:*:*:*:*:*
+supplier: 'Organization: Espressif Systems (Shanghai) CO LTD'
+originator: 'Organization: non-GNU software and documentation, lwIP Project <[email protected]>'
+description: A Lightweight TCP/IP stack with additional features and patches from Espressif.
+cve-exclude-list:
+  - cve: CVE-2020-22284
+    reason: The fix for this vulnerability has been incorporated from the lwIP project upstream as ecd6009a, 6ffe30d9 and 8f5a0aaa.
+  - cve: CVE-2020-22283
+    reason: The fix for this vulnerability has been incorporated from the lwIP project upstream as 379d5504, ba3b04e7 and 843a1161 (Note that this vulnerability is not listed in the NVD against lwip version 2.1.2, but version - N/A).