test: rs-sdk tests refactoring

[lklimek]

Issue being fixed or feature implemented

Structure of rs-sdk tests can be simplified

What was done?

1. Use DPNS contract id, document id, identity id created on genesis instead of asking users to provide them
2. Create rs-sdk .env file during yarn setup process
3. Move Config code around and simplify it
4. Reorganize test-related docs
5. Update docs

How Has This Been Tested?

Run online testing using local network.

Breaking Changes

None

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[shumkov]

Good job! 👍