Derive Clone on Bulk request structs

[jefftt]

Addresses https://github.com/elastic/elasticsearch-rs/issues/195

This option is the least invasive as it doesn't change the type signatures although it requires extra allocations in order to clone the struct. Allowing body to take a reference to a slice of operations instead of ownership would be a more efficient solution that could be addressed in a separate PR

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[cla-checker-service[bot]]

💚 CLA has been signed

[jefftt]

i signed the CLA but not sure github is being updated properly

[jefftt]

oh there we go

[jefftt]

Hi @russcam - any interest in this change?

[russcam]

Hey @jefftt, I no longer work for Elastic so no longer have access rights to this repository to work with you on this PR. Perhaps @swallez or @sethmlarson can work with you to get this in?