Switch Spook to MIT license

Description

This PR switches the license Spook is published with, to an OSI approved open source license: MIT License.

Motivation and Context

I originally started out to create something to experiment with (and I still do experiment concepts with Spook). However, nowadays, Spook seems to be gaining popularity and slowly getting an actual "fan base" (sounds weird to write/say).

I added the passive aggressive license to Spook. The main reason: it is a custom integration; custom integrations should be avoided as much as possible. Additionally, there is stuff in Spook that might not be the best idea.

The current passive aggressive license always leads to questions and discussions, and more often seems to scare people.

Spook 👻 has turned one year old. How it developed and was embraced by part of the community, made me wonder: Is it time to open it up more and change the license?

Based on the results here: https://github.com/frenck/spook/discussions/613

I think a significant amount of voters showed they do care; therefore, this PR is switching Spook to use the MIT license.

How has this been tested?

Screenshots (if appropriate):

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[x] Other

Checklist

[x] My code follows the code style of this project.
[x] My change requires a change to the documentation.
[x] I have updated the documentation accordingly.

frenck / spook