Annif 0.57

Training of NN ensemble models can now be performed in parallel (running suggest operations simultaneously for all source projects) on multiple CPUs; this is controlled by using the --jobs parameter of the train command. The compatibility of Annif with DVC is improved by supporting TOML file format for configuring Annif projects. The --force option is added to the loadvoc command that can be used to replace an existing vocabulary instead of updating it. This release includes many small maintenance tasks for the CI/CD pipeline, e.g. migrating Docker image builds to GitHub Actions from the Drone platform.

Omikuji, TensorFlow and Connexion dependencies are upgraded to the latest available versions; retraining of projects should not be necessary.

New features:
#526/#567 Add --force option to loadvoc CLI command

Improvements:
#429/#568 Perform suggest operations in parallel using multiprocessing in nn_ensemble
#547/#560 Support TOML as a configuration file format alongside CFG/INI for DVC compatibility

Maintenance:
#570 Use fulltext corpus in MLLM tests which is much faster
#571 Docker builds on GitHub Actions CI/CD
#572 Update Dockerfile v0.57
#573 Ensure setuptools and wheel are installed & up-to-date for tests in GitHub Actions CI
#574 Avoid running duplicated tests on PRs in GitHub Actions CI
#575 Resolve some Warnings by tests
#576 Enable pip cache in GitHub Actions CI
#577 Improved Project links in PyPI page
#578 Update dependencies v0.57
#581/#582 Add tags trigger to GH Actions CI/CD workflow