fix: split s3 config by the first delimiter until string end

[javierprovecho]

This PR fix S3 credentials parsing when a pair use an extended charset from AWS official (1). This apply to an scenario when pointing burry to a Minio instance acting as a gateway to Azure Blob Storage, which uses base64 encoding for secret key.

(1): https://docs.aws.amazon.com/general/latest/gr/aws-sec-cred-types.html#access-keys-and-secret-access-keys

[mhausenblas]

Thank you @javierprovecho!