Create and document how to create a long lived access token for instagram

https://developers.facebook.com/docs/instagram-platform/overview

Unfortunately creating long lived access token is kindof a pain and we have to go through a whole login flow to get a short lived token, then request a long lived token.

Annoyingly the long lived token has to be refreshed every 2 months. So we may want to consider using some sort of vault that the code can update when it runs. Otherwise we'll need to run a script manually within every 2 months and update the github secret manually.

I belive we need an `Instagram API setup with Instagram Login` with `Content Publishing` permissions and access level `Standard Access`.

Acceptance Criteria:
- Figure out and propose a solution which will let us make instagram posts via API key in a maintainable way
- Document the process and update the README so that others who want to copy the project and do the same
- Create new github issues based on that info