[Addon] update datadog trait

[Kolossi]

Description of your changes

• syntax error bugfixes
• add the ability to specify mounted volume name
• add the ability to auto-map dependecies using DD_TRACE_SERVICE_MAPPING env var

How has this code been tested?

Used on own cluster.

Checklist

I have:

• Title of the PR starts with type (e.g. [Addon] , [example] or [Doc]).
• Updated/Added any relevant documentation and examples.
• New addon should be put in experimental.
• Update addon should modify the version in metadata.yaml to generate a new version.