[AWS Lambda] Support new environment variables INSTANA_ENDPOINT_URL and INSTANA_AGENT_KEY in addition to the now deprecated variables INSTANA_URL and INSTANA_KEY.
Improve announce cycle by polling for the "agent ready" state once a second, this will bring the delay from "announce" to "agent ready" down from 10 to ~1 seconds for the majority of cases (in particular with the improved agent to be released soon).
Enforce minimum delay of one second between sending snapshot data and the first spans.