Fix types of core getConfig

[tanishqkancharla]

↪️ Pull Request

Previously getConfig was typed in flow as:

getConfig<T>(
    filePaths: Array<FilePath>,
    options: ?{|
      packageKey?: string,
      parse?: boolean,
      exclude?: boolean,
    |},
  ): Promise<?ConfigResultWithFilePath<T>>;

This generates the ts type definition

getConfig<WebsiteContext>(filePaths: string[], options: {
    packageKey?: string | undefined;
    parse?: boolean | undefined;
    exclude?: boolean | undefined;
} | null | undefined): Promise<…>

Unfortunately, this means the second argument is required in typescript when it’s really not. This PR makes it so the corresponding type definitions of typescript mark the argument as optional.

💻 Examples

N/A

🚨 Test instructions

Run npm run build-ts and see if the output correctly generates optional types for getConfig and getConfigFrom.

✔️ PR Todo

• [-] Added/updated unit tests for this change
• [-] Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs