Add Instagram Provider

[aaronsmulktis]

Changes:

• add instagram to README
• add instagram to external.go
• add instagram to settings.go
• add instagram to settings_test.go
• add instagram to configuration.go
• add external_instagram_test.go
• add provider/instagram.go
• add instagram to .env.example

[kangmingtay]

hey @aaronsmulktis, thanks for contributing to this project, at the moment, we don't really have the bandwidth to support adding additional OAuth providers and we intend to support this with a more generic implementation - #451 (comment)

if there's an urgent need to use instagram as an oauth provider - we strongly recommend forking the project and self-hosting for the time being

[aaronsmulktis]

hey @aaronsmulktis, thanks for contributing to this project, at the moment, we don't really have the bandwidth to support adding additional OAuth providers and we intend to support this with a more generic implementation - #451 (comment)

if there's an urgent need to use instagram as an oauth provider - we strongly recommend forking the project and self-hosting for the time being

All good.. Thanks for the quick reply Kang!