Use payout address to map stats

[MakMuftic]

Replaced node ID with node payout address when mapping node stats

PR Checklist

• I have run linter localy
• I have run unit and integration tests locally
• Rebased to dev branch / merged dev
• Updated CHANGELOG.md

Changes

• refactor stats controller + refactor unit tests
• refactor stats collecting functions (inside /internal/stats package) so they map stats on payout addresses + refactor unit tests

Example

Here is a sample response from /api/v1/stats endpoint:

{
    "stats": {
        "5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty": {
            "total_pings": 2630.7830677516004,
            "total_requests": 50
        }
    },
    "fee": 0.1
}

Issues

Closes #135