[Add Gitlab features to BuildStream 01/04]: Milestones

[Agustín Benito Bethencourt <agustin benito codethink co uk>]

Hi,

### Milestones

Milestones allow us to structure all activities in groups and relate these 
group of actions with time frames. This is extremely useful for road-mapping 
and visualization, specially when releases are approaching.

General description of how milestones work on Gitlab: https://docs.gitlab.com/
ee/user/project/milestones/

Proposal: make use of milestones as a high level structure of our activities:
* Create a global milestone for the ongoing work: buildstream_v1.1
* Create another global milestone for the future work: buildstream_v1.2

By creating these two milestones and make them global, that is, available 
across the entire BuildStream Group, we will be able to structure all 
necessary items across every project, including those in the nosoftware 
Subgroup.

Check the examples I have created for the nosoftware Subgroup: <https://
gitlab.com/groups/BuildStream/nosoftware/-/milestones>
* You can see two milestones corresponding to releases available across the 
Subgroup together with two additional milestones, corresponding to events, 
affecting only the repo/project "communication"

Please remember you can find the complete proposal on Gitlab: https://
gitlab.com/BuildStream/nosoftware/alignment/blob/master/
proposal_to_apply_Gitlab_features_to_BuildStream.md

Best Regards


-- 
Agustín Benito Bethencourt
Principal Consultant
Codethink Ltd