Add TLS and Reconfigure TLS

Signed-off-by: Muhammad Raisul Islam Evan <[email protected]>

docs/guides/memcached/reconfigure-tls/_index.md

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+---
+title: Reconfigure Memcached TLS/SSL
+menu:
+  docs_{{ .version }}:
+    identifier: mc-reconfigure-tls
+    name: Reconfigure TLS/SSL
+    parent: mc-memcached-guides
+    weight: 46
+menu_name: docs_{{ .version }}
+---

docs/guides/memcached/reconfigure-tls/overview.md

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+---
+title: Reconfiguring TLS of Memcached
+menu:
+  docs_{{ .version }}:
+    identifier: mc-reconfigure-tls-overview
+    name: Overview
+    parent: mc-reconfigure-tls
+    weight: 10
+menu_name: docs_{{ .version }}
+section_menu_id: guides
+---
+
+> New to KubeDB? Please start [here](/docs/README.md).
+
+# Reconfiguring TLS of Memcached Database
+
+This guide will give an overview on how KubeDB Ops-manager operator reconfigures TLS configuration i.e. add TLS, remove TLS, update issuer/cluster issuer or Certificates and rotate the certificates of a `Memcached` database.
+
+## Before You Begin
+- You should be familiar with the following `KubeDB` concepts:
+  - [Memcached](/docs/guides/memcached/concepts/memcached.md)
+  - [MemcachedOpsRequest](/docs/guides/memcached/concepts/memcached-opsrequest.md)
+
+## How Reconfiguring Memcached TLS Configuration Process Works
+
+The following diagram shows how KubeDB Ops-manager operator reconfigures TLS of a `Memcached` database. Open the image in a new tab to see the enlarged version.
+
+<figure align="center">
+  <img alt="Reconfiguring TLS process of Memcached" src="/docs/images/memcached/memcached-reconfigure-tls.png">
+<figcaption align="center">Fig: Reconfiguring TLS process of Memcached</figcaption>
+</figure>
+
+The Reconfiguring Memcached TLS process consists of the following steps:
+
+1. At first, a user creates a `Memcached` Custom Resource (CR).
+
+2. `KubeDB` Community operator watches the `Memcached` CR.
+
+3. When the operator finds a `Memcached` CR, it creates required number of `PetSets` and related necessary stuff like appbinding, services, etc.
+
+4. Then, in order to reconfigure the TLS configuration of the `Memcached` database the user creates a `MemcachedOpsRequest` CR with the desired version.
+
+5. `KubeDB` Enterprise operator watches the `MemcachedOpsRequest` CR.
+
+6. When it finds a `MemcachedOpsRequest` CR, it halts the `Memcached` object which is referred from the `MemcachedOpsRequest`. So, the `KubeDB` Community operator doesn't perform any operations on the `Memcached` object during the reconfiguring process.  
+
+7. By looking at the target version from `MemcachedOpsRequest` CR, `KubeDB` Enterprise operator will add, remove, update or rotate TLS configuration based on the Ops Request yaml.
+
+8. After successfully reconfiguring `Memcached` object, the `KubeDB` Enterprise operator resumes the `Memcached` object so that the `KubeDB` Community operator can resume its usual operations.
+
+In the next doc, we are going to show a step-by-step guide on updating of a Memcached database using update operation.