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

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[xoriole]

Thank you for your PR @heldersepu.

Instead of passing the config object to RESTManager and rewriting the config as config.api, I think the issue can be solved by simply calling config.write() when the RESTManager has started (in restapi_component.py).

[heldersepu]

@xoriole We debated that in the issue: #8007 (comment)

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.