ElasticRepository Retry on BulkResult error

[niemyjski]

Some items may fail due to version change or multiple bulk results running at the same time. We should retry this and possibly return the number of modified documents (bulkResult.Items). Also, we should invalidate the cache before returning..

https://github.com/exceptionless/Foundatio.Repositories/blob/master/src/Elasticsearch/Repositories/ElasticRepositoryBase.cs#L178

[niemyjski]

@ejsmith looks like what we talked about this morning :)

[niemyjski]

Looks like we need to add

1. the ability to pass a cancel token to a bulk operation
2. return a result of what operations failed or succeed
3. Handle retries when we encounter 429's.