S3A credential provider remapping: make extensible

A new option fs.s3a.aws.credentials.provider.mapping takes a key value pair for automatic mapping of v1 credential providers to v2 credential providers.

Backporting

There's a followup PR to the main patch which should be applied, as it hardens the parser.

HADOOP-18980. Invalid inputs for getTrimmedStringCollectionSplitByEquals (ADDENDUM) (#6546)