Update metadata spec regarding ECS/Fargate pod UIDs

[z1c0]

Description

A recent issue showed that the current spec for parsing Kubernetes pod UIDs does not cover Amazon ECS/Fargate. The existing regex patterns need to be extended.

Spec Issue

• [ ] https://github.com/elastic/apm/issues/677

Agent Issues

• [x] https://github.com/elastic/apm-agent-java/issues/2762
• [x] https://github.com/elastic/apm-agent-dotnet/issues/1805
• [ ] https://github.com/elastic/apm-agent-nodejs/issues/2898
• [ ] https://github.com/elastic/apm-agent-python/issues/1621
• [x] https://github.com/elastic/apm-agent-go/issues/1303
• [ ] https://github.com/elastic/apm-agent-php/issues/756
• [ ] https://github.com/elastic/apm-agent-ruby/issues/1297