Make it compatible with mariadb

[ggpasqualino]

I am really sorry, the last release will break if the client doesn't have postgrex there because it's listed as one of the applications to be started, my bad :/

I have plugged this into an example with myxql to test it now and realized that it can't handle the origin to be read after writing, so I also made it optional.

[izelnakri]

Thanks for your consideration and fix. I will need integration tests to merge these changes. Also I want to point out I was intending to support only postgres. However depending on the tests I'm willing to merge the changes. I will also need to set up the CI correctly it seems.

[izelnakri]

Reading this again, it seems tests are not needed to merge these changes but I would like to have some integration tests on mariadb/on CI if we are going to officially support MariaDB now.