Support DynamoDB as a metadata store

[Minoru OSUKA]

Support DynamoDB as a metadata store

[Mark Wolfe]

I am happy to help with this if needed, I have written https://github.com/wolfeidau/dynalock and worked on other locking projects using dynamodb.

[Minoru OSUKA]

@wolfeidau
Thank you.
Since you seem to be familiar with DynamoDB, this issue will be very easy for you.
I am looking forward to your pull request.

It would be great if you could develop it same as the implementation of etcd here.
https://github.com/mosuka/phalanx/blob/main/metastore/storage.go
https://github.com/mosuka/phalanx/blob/main/metastore/storage_etcd.go

[Mark Wolfe]

I started work on this in #74 the documentation helps a lot.

[Minoru OSUKA]

@wolfeidau Thank you for your contribution! 😄