feat: dynamically register extension settings

[namchuai]

Describe Your Changes

• Extension can register its own settings.

Screenshots

Self Checklist

• Added relevant comments, esp in complex areas
• Updated docs (for bug fixes / features)
• Created issues for follow-up changes or refactoring needed

[louis-jan]

@namchuai. I've updated the Settings API as discussed

override async onLoad(): Promise<void> {
  super.onLoad()

  // Register Settings
  this.registerSettings(SETTINGS)

  // Retrieve API Key Setting
  this.apiKey = await this.getSetting<string>(this.settingName, 'default_value_here')
}

// Update extension logic once setting is updated
onSettingUpdate<T>(key: string, value: T): void {
  if (key === this.settingName) this.apiKey = value as string
}

[louis-jan]