Rename ecmr version "external" column to "created_externally"

Related issues

The column name "external" is a reserved keywork in Microsoft SQL Server. The creation of the table "ecmr_ecmrversion" failed in MSSQL because a property with this name exists.

Acceptance criteria

• Implemented code changes don't diverge from the related issue.
• Documentation reflects the status quo after merge.
• Version number is incremented according to SemVer. (Snapshot versions are not merged/released.)
• Only released versions of dependencies are used (i.e. no snapshot versions).
• Pipeline still works.
• GitLab issue is up-to-date.

If necessary, the following sections have been updated:

• Swagger
• Readme.md
• Documentation

Proposed squash commit message

* The column and property "external" in the entity "ecmr_ecmrversion" was renamed to "created_externally"
* Added maven dependency for mssql driver