Add support for ELB and Lambda URL metadata in lambda integrations

[basepi]

Description

Add support for ELB and Lambda URL metadata in lambda integrations: spec PR

Agent Issues

• [ ] https://github.com/elastic/apm-agent-java/issues/2764
• [ ] https://github.com/elastic/apm-agent-nodejs/issues/2901
• [x] https://github.com/elastic/apm-agent-python/issues/1622