[Task]: Document guidelines for how version guards should be specified for Beam dependencies

### What needs to happen?

We should document this in install_requires and potentially in contributor guide and/or release guide sections of developer docs and have some process that enforces absence of obvious mistakes such as:
- depending on an exact version of a dependency.
- specifying '<=' in upper bound instead of a strict '<'.
- omitting explanations for non-obvious choices, such as a too open or too narrow range.

It might be possible to have a unit test or release validation script that automatically verifies some of that.

### Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

### Issue Components

- [X] Component: Python SDK
- [ ] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam examples
- [ ] Component: Beam playground
- [ ] Component: Beam katas
- [ ] Component: Website
- [ ] Component: Spark Runner
- [ ] Component: Flink Runner
- [ ] Component: Samza Runner
- [ ] Component: Twister2 Runner
- [ ] Component: Hazelcast Jet Runner
- [ ] Component: Google Cloud Dataflow Runner