When displaying the pipelines of a project we now preload the following
data:
1. Authors of the commits that belong to these pipelines
2. The number of warnings per pipeline, which is used by
Ci::Pipeline#has_warnings?
== Commit Authors
Previously this data was queried for every Commit separately, leading to
20 SQL queries being executed in the worst case. With an average of 3 to
5 milliseconds per SQL query this could result in 100 milliseconds being
spent in _just_ getting Commit authors.
To preload this data Commit#author now uses BatchLoader (through
Commit#lazy_author), and a separate module
Gitlab::Ci::Pipeline::Preloader is used to ensure all authors are loaded
before they are used.
== Number of warnings
This changes Ci::Pipeline#has_warnings? so it supports preloading of the
number of warnings per pipeline. This removes the need for executing a
COUNT(*) query for every pipeline just to see if it has any warnings or
not.
