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

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.