[RELEASE] v4.15.0 (#904)

* [RELEASE] v4.15.0

Co-authored-by: Amir Zarrinkafsh <nightah@me.com>

.buildkite/RELEASE.md

@@ -1 +1 @@
-<!-- Current release: 4.14.2 -->
+<!-- Current release: 4.15.0 -->

BREAKING.md

@@ -6,6 +6,23 @@ recommended not to use the 'latest' Docker image tag blindly but pick a version
 and read this documentation before upgrading. This is where you will get information about
 breaking changes and about what you should do to overcome those changes.
 
+## Breaking in v4.15.0
+* Previously if a configuration value did not exist we ignored it. Now we will error if someone has
+specified either an unknown configuration key or one that has changed. In the instance of a changed
+key a more specific error is intended. This may cause some people who have not updated their config
+to see new errors.
+* Authelia now checks the Notifier is configured correctly before becoming available. If the 
+SMTP Notifier is used and the configuration is wrong or there is something wrong with the server
+Authelia will not start. If the File Notifier is used and the file is not writable Authelia will
+not start.
+* Authelia v3 migration tools are being removed in this release due to the length of time which
+has passed since v4 release. Older versions will still be available for migration if needed.
+
+### Deprecation Notice(s)
+* Environment variable secrets are insecure and have been replaced by a file based alternative
+instead of having the plain text secret in the environment variables. In version 4.18.0 the old method
+will be completely removed. Read more in the [docs](https://docs.authelia.com/configuration/secrets.html).
+
 ## Breaking in v4.10.0
 * Revert of `users_filter` purpose. This option now represents the complete search filter again, meaning
 there is no more automatic filter computation based on username. This gives the most flexibility.