[Add Gitlab features to BuildStream 04/04]: Templates

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

Hi,

### Templates

The usage of issues and merge requests templates will have a positive effect 
so creators include the right information in the right order. This not just 
benefits the completeness of issues and MR, but also helps reviewers and those 
who need to act on them. 

The use of templates is particularly beneficial for newcomers and infrequent  
contributors since it sets the right expectations about what information from 
them is required so the ping-pong process with reviewers is minimised.

A third benefit is that templates might include default metadata which not just 
reduces the time spent in adding them to the ticket, but also helps to process 
them when no additional metadata is added by a user.

Templates need to be selected when creating an issue or MR.

Check the information about templates from Gitlab: https://docs.gitlab.com/ee/
user/project/description_templates.html

Proposal: this only applies to issue and merge request templates applied to 
BuildStream Project only.

 * Issues:
        * Default template: unless an issue creator selects a specific template, 
this is the one that will be used.
        * Bug template: template specifically for opening bugs.

 * Merge requests:
        * Default merge request template

The content of each template will be discussed later on.

Check the examples from nosoftware for issue templates:

 * Bug template: https://gitlab.com/BuildStream/nosoftware/alignment/blob/
master/.gitlab/issue_templates/bug.md

 * Task template (as idea for default issue template): https://gitlab.com/
BuildStream/nosoftware/alignment/blob/master/.gitlab/issue_templates/task.md

Please 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