add distributed tracing to php agent resource

[ls-brentsmith]

Add distributed tracing options to php agent resource.

• 'distributed_tracing_enabled' - Defaults to false
• 'distributed_tracing_exclude_newrelic_header' - Default to false

[ls-brentsmith]

@djoos How do you like to handle the cookbook versioning on PRs?

[djoos]

Hi @ls-brentsmith,

please leave the changelog and cookbook versioning bits - https://github.com/djoos-cookbooks/newrelic/blob/master/CONTRIBUTING.md#metadatarb

Hope this helps!

[ls-brentsmith]

@djoos done

[djoos]

Thanks for your contribution @ls-brentsmith!