Fix Instagram OAuth URL formatting and scope separator

[Faisd405]

This pull request updates the Instagram OAuth provider to improve how authentication URLs are built and adjusts the scope separator for compatibility. The main changes focus on ensuring proper URL formatting and parameter encoding.

OAuth URL handling:

• Changed the scopeSeparator from a space to a comma in the Provider class to match Instagram's expected format.
• Added a new buildAuthUrlFromBase method to construct the authentication URL with correctly encoded query parameters using http_build_query and urldecode.
• Updated the getAuthUrl method to use the new buildAuthUrlFromBase method for generating the Instagram authorization URL.

[atymic]

This looks like an AI pr. Can you please link to the docs for these changes?

[Faisd405]

1. For URL formatting, it should exactly match one of the base URIs in the list of valid OAuth URIs.
2. For Scope Operator, it can be a comma-separated list or a URL-encoded space-separated list. I just follow the example from the Facebook Developer Apps

https://developers.facebook.com/docs/instagram-platform/reference/oauth-authorize/