Include support for git-remote-s3

[jorgee]

S3 can be used to store git repositories using the git-remote-s3 implementation of remote helper.

This branch provides support for this S3 repositories as part of the nf-amazon plugin.
It implements a JGit Transport with the Fetch and Push connection as well as the RepositoryProvider, ProviderConfig RepositoryFactory required to support s3 git repositories.
The fetch connection is used to clone and pull branches of the repository in the clone, pull and run commands
The push connection is able to push branches.

Current Limitations:

• Due to a limitation in the access rights of some JGit transport classes, when a branch is pushed it is correctly stored in the remote repository but the local repo refs are not updated with the reference to the remote ref (origin/branch)

TODO:

• Try to fix limitations
• Get defaults from aws config
• Test pull when branch is detached
• Test push non up-to-date branch
• Add unit tests

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