Support client certificates with SolrNet.Cloud. Fixes #591

[kostas-kelgeorgiadis]

Support client certificates with SolrNet.Cloud. Fixes #591.

Usage:

        var cert = LoadCertificate(certificatePath, certificatePass);
        var requestFactory = cert is null
            ? new HttpWebRequestFactory() as IHttpWebRequestFactory
            : new ClientCertificateHttpWebRequestFactory(cert);

        var cloudStateProvider = new SolrNet.Cloud.ZooKeeperClient.SolrCloudStateProvider(zkConnectionString, zooKeeperTimeoutMs: timeoutSeconds * 1000);
        SolrNet.Cloud.Startup.InitAsync<T>(
            cloudStateProvider: cloudStateProvider,
            collectionName: collectionName,
            isPostConnection: true,
            solrOperationsProvider: new ClientCertificateSolrOperationsProvider(requestFactory, timeoutSeconds * 1000))
                .ConfigureAwait(false)
                .GetAwaiter()
                .GetResult();

Also added a new method for resetting the DI, in case the previous initialization has failed:

        SolrNet.Cloud.Startup.Reset();