Reana-cluster

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- Upgrades to Kubernetes 1.16.
- Moves Traefik installation to Helm 3.0.0.
- Creates a new Kubernetes service account for REANA with appropriate
permissions.
- Makes database connection details configurable so that REANA can connect to
databases external to the cluster.
- Adds an interactive mode on cluster initialisation to allow providing
deployment secrets such as OAuth integration, GitLab integration or
external database details.
- Autogenerates deployment secrets if not provided by the administrator at
cluster creation time.
- Adds CERN specific Kerberos configuration files.
- Adds new flag and configuration to optionally deploy with CERN EOS storage.
- Renames ``reana-cluster.yaml`` to ``reana-cluster-minikube.yaml`` for local
developments.
- Adds Python 3.8 support.

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- Upgrades to Kubernetes 1.14, Helm 2.13 and Minikube 1.0.
- Separates cluster infrastructure pods from runtime workflow engine pods that
will be created by workflow controller.
- Adds support for exposing user interactive sessions such as Jupyter notebook
via Traefik ingress controller.
- Introduces configurable CVMFS and CephFS shared volume mounts. Changes
``SHARED_VOLUME_PATH`` to ``/var/reana/``.
- Adds support for optional HTTPS protocol termination at the ``REANA-Server``
component.
- Improves workflow execution queuing and scheduling via ``REANA-Server``
sidecar.
- Removes unused ``REANA-Workflow-Monitor`` component and ``ZeroMQ`` service.
- Enables Flask debugging mode for the cluster development configuration by
setting ``FLASK_ENV`` accordingly.

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- Improves AMQP re-connection handling. Switches from ``pika`` to ``kombu``.
- Enhances test suite and increases code coverage.
- Changes license to MIT.

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- Fixes default storage method to use Local instead of CephFS.

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- Adds configuration and cluster component templates for mounting CephFS volumes.

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- Bug fix in ``reana-cluster status`` command.