Make password and user name requirements configurable

Summary

Fix caosdb/customers/leibniz-zmt/management#95 Implement caosdb/customers/leibniz-zmt/management#94

See also: #121 (closed)

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CHANGELOG.md

@@ -9,8 +9,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+* Configurable requirements for user names and passwords. The default is the old hard-coded configuration.
+
 ### Changed
 
+* Minimal changes to the error messages for invalid user names and passwords.
+
 ### Deprecated
 
 ### Removed