Fix unarchive mistake in projects API documentation 

import_url migration performance improvements

 Nullifying empty import_urls upfront so the number of projects with import_url not NULL decreases to 1/5.

 Also, now processing batches in blocks of 1000, with a threaded process - a bit experimental.

See merge request !5149

 Nullifying empty import_urls upfront so the number of projects with import_url not NULL decreases to 1/5.

 Also, now processing batches in blocks of 1000, with a threaded process - a bit experimental.

Added setting to set new users by default as external

## What does this MR do?
This implements the feature request #14508. It adds an option in the application settings to set new users by default as external.

## Are there points in the code the reviewer needs to double check?
Everything. Like I mentioned in the discussion of the issue my knowledge of Ruby basically doesn't exists. I tested it on my machine and it seems to work, but as I am very unexperienced in Ruby I highly recommend to  take a close look at the code.

## Why was this MR needed?
It was requested by @DouweM to work on the issue with the proposed changes by me.

## What are the relevant issue numbers?
This MR is for the issue #14508 that followed up after the implementation of #4009.

See merge request !4545

Link to the user's profile in the abuse reports

Link to the user's profile in the abuse reports and add a link to the
admin area view if the user viewing the profile is an admin

Fixes #9127

See merge request !5118

This reverts commit bf2a86b7.

Upgrade oauth2 from 1.0.0 to 1.2.0.

Changelog: https://github.com/intridea/oauth2/compare/v1.0.0...v1.2.0

Follow-up on !3434 since 1.2.0 doesn't limit the JWT version we can use.

Adds support for Rails 5. Working toward #14286.

See merge request !5041

Use scope rather than class method

## What does this MR do?

Use scope rather than class method

## Why was this MR needed?

I assume this would be useful and more clear.

See merge request !5133

Prefer ref rather than id because id is shadowing database id

## What does this MR do?

Just a local variable renaming.

## Why was this MR needed?

Prefer ref rather than id because id is shadowing database id.

See merge request !5134