Mongodb TLS (#1456)

* Support for secure TLS communication in MongoDB, MongoDB Monitoring
Agent and MongoDB Backup Agent
- Move from Golang to Bash for entrypoint program
- Update image tag to 2.0 for Backup and Monitoring Agents and to
3.4.4 for MongoDB
- Add documentation

* changed title & rewrote Step 1 of workflow.rst

* copy-edited ca-installation.rst

* copy-edited & modified structure of workflow.rst

* moved repeated Easy-RSA install & config docs to new page

* edited the sentences describing the Easy-RSA dirs

* copy-edited the page about generating server certificate

* copy-edited the page about generating client certificate

* renamed page to 'How to Set Up a Self-Signed Certificate Authority'

* copy-edited page about how to revoke a certificate

* Comments on how to uniquely name all instances in the cluster

* Added comments about the other questions when setting up a CA

* Added note about one Agent Api Key per Cloud Manager backup

* docs: clarified instructions for generating server CSR

* docs: added back 'from your PKI infrastructure'

* docs: fixed step & added step re/ FQDNs & certs in workflow.rst

* docs: added note re/ the Distinguished Name

* Update docs for env vars setup

* docs: added tip: how to get help with the easyrsa command

docs/server/source/cloud-deployment-templates/first-node.rst

@@ -457,7 +457,7 @@ Step 17. Verify that the Cluster is Correctly Set Up
 
         curl -X GET https://ngx-instance-0
   
-  * Check the MongoDB monitoring and backup agent on the MOngoDB Coud Manager portal to verify they are working fine.
+  * Check the MongoDB monitoring and backup agent on the MongoDB Coud Manager portal to verify they are working fine.
   
   * Send some transactions to BigchainDB and verify it's up and running!