Resolve "store eSeal metadata in the database"

Related issues

Closes #81 (closed)

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

Add Metadata table and persistence entity

- Created a new Liquibase changeset to add the 'metadata' table 
  with fields for 'sealer' and 'timestamp'.
- Implemented the EcmrSealingMetadataEntity class for persistence of eCMR Sealing metadata information.

Co-authored-by: Burczyk, Niklas <niklas.burczyk@iml.fraunhofer.de>
Co-authored-by: Gebel, Lisa <lisa.gebel@iml.fraunhofer.de>

Closes #81 (closed)