Add support for Spacelift (spacectl)

[damianstasik]

Overview

This PR introduces support for spacectl through API Keys. You need to pass your endpoint URL, API Key ID and Secret, that's it!

Type of change

• [x] Created a new plugin
• [ ] Improved an existing plugin
• [ ] Fixed a bug in an existing plugin
• [ ] Improved contributor utilities or experience

How To Test

There's a handy command to test if the credentials are indeed provisioned:

spacectl whoami

The output should contain JSON with the ID and name of the API Key as well as the endpoint URL.

Changelog

[AndyTitu]

Hey @damianstasik , could we help you move this forward in any way?

[damianstasik]

@AndyTitu hey, sorry for the long delay, I'll be taking a look at it today!

[damianstasik]

@arunsathiya thank you for your review, and again sorry for long delay! I've applied your suggestions and finalized the api key importer, works great on my end! Let me know if this is closer to being shippable :)

[AndyTitu]

Hey @damianstasik could you please sign your first few commits as well so we could merge this?

[damianstasik]

@AndyTitu done, thanks for taking a look at this PR!

[sethidden]

@AndyTitu Hey I've just come across this PR as a bystander and it seems like everything is ready to go but it wasn't merged. Is there anything blocking?