Add MetadataDynamicCoder to support encode-decode for new fields in Metatdata

This Issue is to solve similar problems to wha I had in [BEAM-12883.](https://issues.apache.org/jira/browse/BEAM-12883?page=com.atlassian.jira.plugin.system.issuetabpanels%3Aall-tabpanel)

Currently there are 2 Coders for Metadata: default one: org.apache.beam.sdk.io.fs.MetadataCoder and enhanced one org.apache.beam.sdk.io.fs.MetadataCoderV2, the last can also decode-encode lastModifiedMillis and it is done in a new coder in order to support backward compatibility.

This will be hard to maintain, we will need to create a new coder for any new field that will be added to Metadata.

So, as suggested in this [comment: #15510](https://github.com/apache/beam/pull/15510#issuecomment-928390587), we need to have some new generic coder : MetadataDynamicCoder.

MetadataDynamicCoder can decode/encode any new fields added to Metadata by sending getter, setter and coder.

Imported from Jira [BEAM-13640](https://issues.apache.org/jira/browse/BEAM-13640). Original Jira may contain additional context.
Reported by: brachi_packter.