refactor: use generic PSR-7 as a `HTTP` client

[bednar]

Closes #120

Proposed Changes

Uses https://www.php-fig.org/psr/psr-7/ as a HTTP client instead strong depends to Guzzle.

Checklist

• [ ] CHANGELOG.md updated
• [x] Rebased/mergeable
• [x] A test has been added if appropriate
• [ ] make test completes successfully
• [x] Commit messages are conventional
• [x] Sign CLA (if not already signed)