[Add Gitlab features to BuildStream 03/04]: Issue Boards

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

Hi,

### Issue Boards

Boards allow you to visualise and manage issues in a simple way. Several 
boards can be created for each Group, Subgroup and Project to meet different 
user profile needs. But the key feature is that issue boards will allow 
BuildStream to create simple workflows so managing issues states or severity 
can be done by simply moving the issues within the board.

Check the description of labels on Gitlab: https://about.gitlab.com/features/
issueboard/

Check how to create simple workflows: https://docs.gitlab.com/ee/user/project/
issue_board.html#creating-workflows

Proposal: taking advantage of the proposed milestones as well as the state and 
the severity labels, we will create at least the following 2 set of boards at 
the BuildStream Group level:

 * Workflow boards:
        * Per milestone.
                * Check this example from nosoftware: https://gitlab.com/groups/
BuildStream/nosoftware/-/boards/567536?milestone_title=BuildStream_v1.1&=
        * All tickets
                * Check this example from nosoftware: https://gitlab.com/groups/
BuildStream/nosoftware/-/boards?= 
        * Just critical issues.
                * Check this example from nosoftware: https://gitlab.com/groups/
BuildStream/nosoftware/-/boards/567534?=&label_name[]=Critical
        * Just bugs.
                * Here you can see an example from gitlab: 
https://gitlab.com/gitlab-org/gitlab-ce/boards/353106?=&label_name[]=bug

 * Severity boards:
        * Per milestone: only current and future milestones, so two boards.
        * All tickets
                * Check the example from nosoftware: https://gitlab.com/groups/
BuildStream/nosoftware/-/boards/567539?=
        * Just bugs.

Similar boards will be created for the BuildStream Project, so only technical 
issues would be visualized in those.

Please remember you can read the full 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