Release 0.1.5 version

When I released the 0.1.4 version I accidentally forgot to change the values for tag in values.yaml, so that is still using the 0.1.3 version images. For this reason alone, we should release a new version that actually includes the improvements that 0.1.4 introduced (because it needs the new docker containers)

Also, there were like 5 MRs merged yesterday, so that's a good reason to release 0.1.5 as well.

Release procedure

When releasing a new version of the wordpress-helm chart, please remember to do the following:

• update CHANGELOG.md;
• change the chart version in Chart.yaml;
• change the default image.tag and initImage.tag in values.yaml to the new version (e.g., "0.1.3");
• create a git tag for the new version (e.g., "0.1.3") and push it to Gitlab (any branch will do); the CI will create and push docker images tagged by that same version string. (You can push all git tags using git push --tags, or this specific one using git push origin 0.1.3.)