feat: add support for a credentials chain for minio access (#31051)

We wanted to be able to use the IAM role provided by the EC2 instance
metadata in order to access S3 via the Minio configuration. To do this,
a new credentials chain is added that will check the following locations
for credentials when an access key is not provided. In priority order,
they are:

1. MINIO_ prefixed environment variables
2. AWS_ prefixed environment variables
3. a minio credentials file
4. an aws credentials file
5. EC2 instance metadata

(cherry picked from commit c0880e7695346997c6a93f05cd01634cb3ad03ee)

Conflicts:
	docs/content/administration/config-cheat-sheet.en-us.md
	does not exist in Forgejo

modules/storage/testdata/aws_credentials

@@ -0,0 +1,3 @@
+[default]
+aws_access_key_id=ExampleAccessKeyIDAWSFile
+aws_secret_access_key=ExampleSecretAccessKeyIDAWSFile

modules/storage/testdata/minio.json

@@ -0,0 +1,12 @@
+{
+        "version": "10",
+        "aliases": {
+                "s3": {
+                        "url": "https://s3.amazonaws.com",
+                        "accessKey": "ExampleAccessKeyIDMinioFile",
+                        "secretKey": "ExampleSecretAccessKeyIDMinioFile",
+                        "api": "S3v4",
+                        "path": "dns"
+                }
+        }
+}