[CL]: Create testing_strategy.md

[AlpinYukseloglu]

Background

Given all the functional tests we have been adding lately, it would be extremely valuable to have a single place where we track the primary behaviors being tested. This would serve two main purposes:

1. Help us identify more edge behaviors we need to test
2. Make our code/tests easier to onboard to and review

Suggested Design

• Have a section on high level testing strategy for unit tests
• Break down specific categories of behavior covered by various functional tests
• Move large comment blocks from test comments to this file (e.g. https://github.com/osmosis-labs/osmosis/pull/5526/files#diff-178c1d7e40dc447c9e54f31d86b1ff1ddf5ede3eb7dbae54d1afce17562aa4efR155-R227)

Acceptance Criteria

• Testing strategy for all core CL functionality is well understood and well explained