Support to additional credential provider

Hi hunde.keba, we are working on integrate key module with s3fs https://www.drupal.org/project/s3fs/issues/2976430
You can reed more of key module in:
- https://www.drupal.org/project/key
- https://www.drupal.org/docs/8/modules/key

We have a case where we are using the latest version of the module which is currently `
API version
s3fs 8.x-3.0-alpha13
By jansete on 9 July 2018 `

The provided patch doesn't work for us.

We have made the required changes to match `
API version
s3fs 8.x-3.0-alpha13
By jansete on 9 July 2018 ` Patch file has been added.

I've extended this patch by extra condition in s3fs_requirements() becasue at admin/reports/status page warning message was displayed with misconfiguration.

Here with Cache Support (Thanks to Florian Weber).

rerolled with config form item (tests should now pass apart from Drupal9 Deprecation warnings).

I believe this should be fixed by the changes made in #3121830: Use CredentialProvider::defaultProvider rather than individual providers

Configuration now allows the use of a custom INI or using DefaultProvider which makes use of Credentials by default.

Thanks to @zuernBernhard for the caching support comments as It showed me I needed to look at caching the credentials. I brought that forward in its own patch in commit b12088184 as well without making it a hard dependency. My apologies though that I forgot to add your name into the commit subject.

New patch for alpha17

@dawid_nawrot

Just to double check is this because https://git.drupalcode.org/project/s3fs/-/commit/72f23193028d26f85e1f13b... from #3121830: Use CredentialProvider::defaultProvider rather than individual providers doesn't actually solve this issue or is the reroll for continuity from how you were using it in Alpha16 and wanting to keep it the same in Alpha17?

@cmlara

the second option, it looks like patch from #12 doesn't work anymore for alpha17, so I've updated it and now it patches the module flawlessly. TBH, I had no idea about ini credentials file approach patch.

Thanks @dawid_nawrot, I just wanted to make sure it wasn't a confirmed fault.

If you do get a chance to load it up in a lab environment I would encourage giving it a test. That patch should allow you to just deploy (as long as you don't have a secret_key or settings_key) and pickup ecs credentials without any INI configs needed.

Updated to work with 8.x-3.0-beta4