make the readme a little more easy to use

[fanimali]

Hello, i think that the previous version of the readme was much easier to use and allowed for quicker setup of the entire application. I would like to put back this block:

Running the app
First start the Provider app using command java -cp target/producer_failover-*-jar-with-dependencies.jar com.datastax.demo.streaming.provider.ClusterConfigProvider

Then start the Producer app using command java -cp target/producer_failover-*-jar-with-dependencies.jar com.datastax.demo.streaming.producer.ProducerApp

Finally start the Consumer app using command java -cp target/producer_failover-*-jar-with-dependencies.jar com.datastax.demo.streaming.consumer.ConsumerApp

Performing failover
The above demo app uses two Astra Streaming SaaS clusters (ideally deployed in different regions) with bidirectional replication. Internally it refers to them as clusterA and clusterB. Initially, clusterA is the default Primary and clusterB is DR/Failover.

You can find which cluster is currently Primary at anytime by hitting the Provider endpoint at /getConfig. If you are running the app locally, it can be accessed here http://localhost:8080/getconfig

To inject a failover, go to Provider endpoint /setConfig and pass the url param cluster-name with a value of the clusterA OR clusterB based on the cluster you want to failover to.

If running locally, you could initiate a failover hitting endpoint http://localhost:8080/setconfig?cluster-name=clusterB

[abhigo-ds]

@fanimali, thank you for the input.
Please see the details below:

• This app is different from the pulsar-failover-demo hence the different style of readme.
• This is a springboot app, so most of the modules(producer/consumer) will come up systematically as part of the application run process. I missed adding information on additional producers and consumers. It is available now with the commit.
• Also, the client application and the provider application are two separate applications. Due to this, the failover information is available under the provider application README.

Please review this and let me know.