adding bulkinsert support

[Jeevananthan-23]

Close #238 - Adding a feature to Bulk Insert data into Redis with the help of pipelines.

[slorello89]

1. This should yield the IDs of the items inserted into Redis. Not the full KeyNames, just the ids. That should be returned by the call to Set within the method.
2. This should just be named Insert and should just overload the regular behavior.
3. This should have an overload to accept a timespan so folks can do TTL with it.

[Jeevananthan-23]

@slorello89, I got your point here this method should return List<string> ids this must be the behavior of the method but the issue is with Call to Set within this method. Because the method is a Task typo which accepts it not a string type.

 /// <inheritdoc/>
        public async Task<List<string>> Insert(IEnumerable<T> items, TimeSpan timeSpan)
        {
            var tasks = new List<Task<string>>();
            foreach (var item in items.Distinct())
            {
                tasks.Add(_connection.SetAsync(item, timeSpan));
            }

            await Task.WhenAll(tasks);
            var result = tasks.Select(x => x.Result).ToList();
            return result;
        }

[slorello89]

@Jeevananthan-23 Thanks for submitting this, couple of comments about what the api should look like (also looks like a lot of stylistic stuff in the test class which distracts from what's going on in it).

[slorello89]

LGTM 👍 thanks for submitting this @Jeevananthan-23 :)