[keycloak-dev] Move wiki pages to keycloak/docs

[Stian Thorgersen]

For developer related docs, for example:

* Release process
* Release manual testing
* Upgrading database schema
* Upgrading OpenShift cartridge

I propose we stop using the GitHub wiki and instead add it to https://github.com/keycloak/keycloak/misc. We can add a link to the docs in the main https://github.com/keycloak/keycloak/README.md.