and drop exception handling around HealthCheck::Utils.process_checks, it wasn't needed

delete the enabled_oauth_sign_in_sources after getting it's value into enabled_oauth_sign_in_sources

just delete enabled_oauth_sign_in_sources and get it's value

On Application Settings Page let the user select the enabled OAuth Sign in sources instead of the disabled ones

`User#starred_projects` doesn't perform any visibility checks. This has
a couple of problems:

1. It assumes a user can always view all of their starred projects in
   perpetuity (project not changed to private, access revoked, etc.).
2. It assumes that we'll only ever allow a user to star a project they
   can view. This is currently the case, but bugs happen.

Add `User#viewable_starred_projects` to filter the starred projects by
those the user either has explicit access to, or are public or
internal. Then use that in all places where we list the user's starred
projects.

Also added a health check page to the admin section for resetting the token.

We send a state of ansi2html to client, client needs to send this state back.
The state describes the configuration of generator and position within trace.

Closes gitlab-org/gitlab-ee#536

I wanted to share what I learned trying to debug web hooks using
netcat.

Codestyle changes to easy EE merge

Closes #15533

Closes #15527.
Signed-off-by: NRémy Coutable <remy@rymai.me>

- Parameter validation as ISO8601 format

This button depends on Issue#can_be_worked_on? which in turn depends on
Issue#related_branches. By rendering this button asynchronously we can
finally remove all usages of Issue#related_branches and
Issue#referenced_merge_requests from the issues "show" page.

Changed some variable names
Fixed CHANGELOG entry

CHANGELOG item

Closes #13992

Closes #15515

Closes #4228

Add due_date text field to sidebar issue#show
Add ability sorting issues by due date ASC and DESC
Add ability to filtering issues by No Due Date, Any Due Date, Due to tomorrow, Due in this week options
Add handling issue due_date field for MergeRequest
Update CHANGELOG
Fix ambigous match for issues#show sidebar
Fix SCREAMING_SNAKE_CASE offenses for due date contants
Add specs for due date sorting and filtering on issues