Chore/k6 testing

[Andreass2]

Description

Added a k6 load testing script. It can be run with docker, so you do not need to install k6 locally on your computer.

• Fixed that slow transfers were canceled.
• Fixed missing garbage collection of database connections
• Don't process fileRetention change if its already has the given value.

Related Issue(s)

• Ytelsestest #334

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[Ceredron]

I was surprised with how the .js file was put into the .NET project, but it ended up working great with Visual Studio.

It was easy to setup. Can maybe add a comment in the README about replacing variables in the .js file.

I'm getting about ~550 iterations/minute to the Test environment now with the dummy text file. Less than I expected! Looking forward to playing around with it more.

[Ceredron]

This was during load test. DB connection leak fix worked for sure, nice!