[pyclustering.cluster.dbscan][ccore.dbscan] Custom distance metric

**Introduction**
DBSCAN algorithm should be able to accept distance metric in the same way as K-Means, K-Medians, etc.

**Description**
- [ ] Introduce new optional argument `metric` (`distance_metric` type) under `**kwargs` for Python version of the library.
- [ ] Introduce new optional argument `metric` with new or updated constructor for C++ version of the library.
- [ ] Support from KD-tree is required to support that feature.
- [ ] Unit-tests for the custom distance matrix for Python pyclustering version.
- [ ] Unit-tests for the custom distance matrix for C++ pyclustering version.
- [ ] Documentation examples for C++ version.
- [ ] Documentation examples for Python version.

**Links**
- Proposal link: #582
- The issue depends on: #583