Refactor RESTManager and add config.write when port changes

[heldersepu]

With this change the http_port is updated as soon as it changes fixes #8007

[github-actions[bot]]

Hi @heldersepu, thank you for contributing to Tribler! 🚀

This PR was created by an outside collaborator, so some checks were not run for security reasons. To trigger the full set of checks, any member of the Tribler team can add the label PR: safe to check to the current PR.

[heldersepu]

@xoriole We debated that in the issue: https://github.com/Tribler/tribler/issues/8007#issuecomment-2100938488

in a nutshell:

• That config was not a real config(TriblerConfig) but of type APISettings, bad name
• No need for two params: config=config.api, state_dir=config.state_dir that can be just one
• This way we only invoke the write only when necessary.