skip cert writing and variable setting if concat certs starts with ;

[msarahan]

The problem being approached here is how to handle the absence of certificates. The input of certificates looks like:

        with:
          cert_concat: "${{ secrets.OTEL_EXPORTER_OTLP_CA_CERTIFICATE }};${{ secrets.OTEL_EXPORTER_OTLP_CLIENT_CERTIFICATE }};${{ secrets.OTEL_EXPORTER_OTLP_CLIENT_KEY }}"

If these secrets are not set, they'll just evaluate as empty, so our cert_concat value should come out looking like ;;. This startsWith test should work, as should many other simple string comparisons. The cleanest way is probably to try a different way of setting the input to cert_concat, such that it is an empty string when the variables are not set. That is left for a future exercise, because this cert code is likely to go away soon anyway. We don't really want to be using certs.