Move the Flask config override to Invenio-Config-TUW

The current versions of invenio-accounts and invenio-oauthclient (both v2.0.1) use the same 'blueprint.record_once' mechanism to modify the config values, leading to race conditions with our hack. So we decided to revert the mechanism to the older app.before_first_request and move the logic to Invenio-Config-TUW.