[DD] Improve the deployment version info by introducing a new data point from GoCD

[jristau1984]

When looking at the LMS incident on June 3, there was a deployment in Stage that was of the same version with different configuration. This was invisible in DataDog, so we want to introduce a new piece of data which can highlight when a deployment happens that is of the same edx-platform version.

[robrap]

@timmc-edx: [inform]

1. I'm moving this to the pipeline epic to be considered in the future.
2. I closed two duplicate tickets that were mentioned on this one (DD version tag improvements for edxapp #751, Enhance DD version tag for edx-edxapp-lms #707). Someone could take a quick peak to see if there is anything worth bringing over.

[timmc-edx]

Sounds good. Responding to something on one of those issues -- I think we'll need to introduce a new tag rather than augment version, since I believe version has to just be the commit hash (if we want source code linking).