[FEATURE] - cardano-testnet documentation

[CarlosLopezDeLara]

What

Add cardano-testnet documentation to developers.cardano.org

Why

There is no user documentation.

Acceptance Criteria

1. A new section is added to developers.cardano.org at the same level of cardano-node and cardano-cli
2. Documentation includes:

• How to initialize a cluster
• Configurations required
• Troubleshooting most frequent issues

Personas

• SPOs
• dApp Devs
• Exchanges
• Wallets
• 3rd party tools
• ADA holders

Definition of Done (DoD)

• Acceptance Criteria + User Stories & DoD created and singed-off (by PO, dev & test owners)
• Builds successfully on CI
• Code & Test review (as per Acceptance Criteria)
• There is documentation and/or examples for the new functionality (usage/response)
• Log/record changes on Vnext (or similar depending on what we adopt)
• Ticket number(s) included in PR description
• All Acceptance Criteria met and covered by dev/unit/property/integration tests
• System/E2E automated tests + System Test Engineer Owner Sign-off

NOTE: Ideally, we should merge only fully implemented and tested features into the master branch.
So all the above steps are required for the PR to be merged.
In order to avoid the PRs becoming stale and requiring to be rebased on master, these can be merged
after a reasonable time (current agreement is 3 days) if the System Test Engineer Owner's sign-off
was not provided (last step in the DoD).

IMPORTANT: Any deviation from the plan should be discussed and agreed as a comment in the Feature file.

Sign-off

• Product Owner
• Dev Owner
• System Test Engineer Owner

Related PRs

1. PR # here