add option to bypass certificate validation

[SylvainJuge]

Fixes #493

Mostly a copy of the equivalent feature in classic agent.

tested manually with:

• dummy keystore (included in PR) without any root CA in it
• configure keystore on test application with javax.net.ssl.keyStore and javax.net.ssl.keyStorePassword JVM settings + add agent + start application
• see lots of SSL related exceptions with SunCertPathBuilderException: unable to find valid certification path to requested target
• set ELASTIC_OTEL_VERIFY_SERVER_CERT environment variable to false
• restart the app and see that no more SSL related exception is throws, data should arrive at expected endpoint.