Testing: Add page about software testing with CrateDB (Java and Python)

[amotl]

About

This patch adds a dedicated page which is indexing a few resources about software integration testing with Java and Python.

• native: Python unittest, using cr8
• native: pytest-crate, using cr8
• testcontainers: Testcontainers for Java
• testcontainers: Testcontainers for Python (pytest and unittest)

References

• https://github.com/crate/cratedb-examples/pull/280

Preview

• https://crate-clients-tools--80.org.readthedocs.build/en/80/#id1
• https://crate-clients-tools--80.org.readthedocs.build/en/80/integrate/testing.html

/cc @karynzv, @hlcianfagna, @marijaselakovic, @seut