Add Option to choose backend base url for studio sync

[LilithWittmann]

Is your feature request related to a problem? Please describe. Studio users are using different instances of the studio backend. That might be either customers on a specific studio instance (e.g. for a certain geography or for their enterprise) or the studio engineering/product team testing integrations with our figma plugin.

Another option could be also to have on every studio instance an api endpoint /.well-known/plugin-config.json. Where we put all instance specific feature flags/urls in. And instead of just taking the base url and replacing it having a config object that maybe looks something like that

{
    "API_URL": "https://api.acme-corp.enterprise.tokens.studio",
    "CLIENT_ID": "1233445",
    "FEATURE_FLAGS": {
         "realtime_sync": true,
         "oauth_device_flow": true
    }
}

Describe the solution you'd like In the studio sync provider there should be an option to enter a base url (e.g. http://app.acme-corp.enterprise.tokens.studio/) which then is used to communicate with instead of the default studio base url. This url should be editable later in the configuration too.

Describe alternatives you've considered As we will have more and more different integration the current approach of doing a plugin build when doing testing - especially with feature branches of our backends - becomes a bit too much effort to do continuously.

Additional context Add any other context or screenshots about the feature request here.

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[drwpow]

Lint errors are in main, and are for files not touched in this PR.

[drwpow]

Going to merge & test. Happy to fix any issues in a followup!