Merge branch 'feature/precalculate-authorized-projects' into 'master'

Precalculate authorized projects in database

## What does this MR do?
It caches user's authorized projects in database instead of using multiple unions, which should simplify and speed-up things since this operation (getting authorized projects) is used a lot.

## Are there points in the code the reviewer needs to double check?
Did we miss a scenario where we need to refresh the list of projects?

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
#23150 

See merge request !6839

3 files changed, 11 insertions, 0 deletions

diff --git a/db/fixtures/development/04_project.rb b/db/fixtures/development/04_project.rb
index a984eda5ab5..18a2df7c059 100644
--- a/db/fixtures/development/04_project.rb
+++ b/db/fixtures/development/04_project.rb
@@ -1,4 +1,5 @@
 require 'sidekiq/testing'
+require './db/fixtures/support/serialized_transaction'
 
 Sidekiq::Testing.inline! do
   Gitlab::Seeder.quiet do
diff --git a/db/fixtures/development/17_cycle_analytics.rb b/db/fixtures/development/17_cycle_analytics.rb
index 916ee8dbac8..7b3908fae98 100644
--- a/db/fixtures/development/17_cycle_analytics.rb
+++ b/db/fixtures/development/17_cycle_analytics.rb
@@ -1,5 +1,6 @@
 require 'sidekiq/testing'
 require './spec/support/test_env'
+require './db/fixtures/support/serialized_transaction'
 
 class Gitlab::Seeder::CycleAnalytics
   def initialize(project, perf: false)
diff --git a/db/fixtures/support/serialized_transaction.rb b/db/fixtures/support/serialized_transaction.rb
new file mode 100644
index 00000000000..d3305b661e5
--- /dev/null
+++ b/db/fixtures/support/serialized_transaction.rb
@@ -0,0 +1,9 @@
+require 'gitlab/database'
+
+module Gitlab
+  module Database
+    def self.serialized_transaction
+      connection.transaction { yield }
+    end
+  end
+end