Add FOSSA badges (open-telemetry#3280)

Author: marcalff

README.md

@@ -5,6 +5,8 @@
 [![Build
 Status](https://github.com/open-telemetry/opentelemetry-cpp/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/open-telemetry/opentelemetry-cpp/actions)
 [![Release](https://img.shields.io/github/v/release/open-telemetry/opentelemetry-cpp?include_prereleases&style=)](https://github.com/open-telemetry/opentelemetry-cpp/releases/)
+[![FOSSA License Status](https://app.fossa.com/api/projects/custom%2B162%2Fgithub.com%2Fopen-telemetry%2Fopentelemetry-cpp.svg?type=shield&issueType=license)](https://app.fossa.com/projects/custom%2B162%2Fgithub.com%2Fopen-telemetry%2Fopentelemetry-cpp?ref=badge_shield&issueType=license)
+[![FOSSA Security Status](https://app.fossa.com/api/projects/custom%2B162%2Fgithub.com%2Fopen-telemetry%2Fopentelemetry-cpp.svg?type=shield&issueType=security)](https://app.fossa.com/projects/custom%2B162%2Fgithub.com%2Fopen-telemetry%2Fopentelemetry-cpp?ref=badge_shield&issueType=security)
 
 The C++ [OpenTelemetry](https://opentelemetry.io/) client.