Update documentation to include more information on Cloudflare R2 credentials

[OphidieDev]

What type of feature request is this?

• Mantle doesn't support a Roblox feature I would like to use
• Mantle CLI improvement
• Other

Describe your problem
Mantle documentation does not specify that Cloudflare R2 credentials can be sent through the ordinary "MANTLE_AWS_ACCESS_KEY_ID" and "MANTLE_AWS_SECRET_ACCESS_KEY" env variables. These env variables imply that they are exclusive to an AWS setup. I had to look through a previous issue to find this solution: #194.

Describe the solution you'd like
Describe how to input R2 credentials within the AWS credential indexes within one or both of these two:
https://mantledeploy.vercel.app/docs/remote-state/cloudflare-r2
https://mantledeploy.vercel.app/docs/authentication

[blake-mealey]

This is already documented here: https://mantledeploy.vercel.app/docs/remote-state/cloudflare-r2

[OphidieDev]

This is already documented here: https://mantledeploy.vercel.app/docs/remote-state/cloudflare-r2

The documentation only mentions how to get the two keys described in the original post:
"To get your credentials, go to the R2 Overview page on Cloudflare, and navigate to "Manage R2 API Tokens". Create a new token with the "Object Read & Write" permissions and apply it to your bucket. Once created, you will see a couple of secrets. You'll need to use the "Access Key ID" and "Secret Access Key" for Mantle."

It then directs you to the authentication page which makes no explicit mention of how the two env variables can be used with Cloudflare R2 and AWS interchangeably and exclusively discusses how to pass these values in the context of an AWS setup.

I'd just hope for a clarifying message on either of these pages letting Cloudflare R2 users know there isn't another set of env variables for people using R2 and that they can be used interchangeably regardless of the true underlying provider.

[blake-mealey]

Makes sense. Feel free to open a PR to add clarification.

[OphidieDev]

Makes sense. Feel free to open a PR to add clarification.

All done! #241