doc: zdb package documentation (#76)

Author: RawanMostafa08

docs/internals/zdb/readme.md

@@ -0,0 +1,71 @@
+# ZDB Module
+
+## Introduction
+
+Package zdb provides a Go client for interacting with [0-DB](https://github.com/threefoldtech/0-DB), which is an efficient key-value store.
+The package offers a simple API for creating, managing, and inspecting 0-DB namespaces abstracting manual Redis commands, in order to control namespace size limits, running modes, passwords, and public visibility.
+
+
+## Interface
+
+A namespace is a complete set of key/data. Each namespace can be optionally protected by a password and size limited.
+You are always attached to a namespace, by default, it's namespace `default`.
+```go
+type Namespace struct {
+    Name              string         `yaml:"name"`                     // The namespace name
+    DataLimit         gridtypes.Unit `yaml:"data_limits_bytes"`        // Maximum data size in bytes
+    DataDiskFreespace gridtypes.Unit `yaml:"data_disk_freespace_bytes"`// Disk space available in bytes
+    Mode              string         `yaml:"mode"`                     // Running mode (user or seq)
+    PasswordProtected bool           `yaml:"password"`                 // Whether password protection is enabled
+    Public            bool           `yaml:"public"`                   // Whether the namespace is public
+}
+```
+
+The zdb package exposes a `Client` interface that defines all 0-DB operations, including creating a 0-DB connection, managing namespaces, configuration, and retrieving database size.
+
+```go
+type Client interface {
+    // Connect creates the connection pool and verifies connectivity by pinging the 0-DB server.
+	Connect() error
+
+    // Close releases the resources used by the client.
+	Close() error
+
+    // CreateNamespace creates a new namespace. Only admin can do this.
+    // By default, a namespace is not password protected, is public and not size limited.
+	CreateNamespace(name string) error
+
+    // Exist checks if namespace exists
+	Exist(name string) (bool, error)
+
+    // DeleteNamespace deletes a namespace. Only admin can do this.
+    // You can't remove the namespace you're currently using.
+    // Any other clients using this namespace will be moved to a special state, awaiting to be disconnected.
+	DeleteNamespace(name string) error
+
+    // Namespaces returns a slice of all available namespaces name.
+	Namespaces() ([]string, error)
+
+    // Namespace retrieves returns basic informations about a specific namespace
+	Namespace(name string) (Namespace, error)
+
+    // NamespaceSetSize sets the maximum size in bytes, of the namespace's data set
+	NamespaceSetSize(name string, size uint64) error
+
+    // NamespaceSetPassword locks the namespace by a password, use * password to clear it
+	NamespaceSetPassword(name, password string) error
+
+    // NamespaceSetMode sets the mode of the namespace
+	NamespaceSetMode(name, mode string) error
+
+    // NamespaceSetPublic changes the public flag, a public namespace can be read-only if a password is set
+	NamespaceSetPublic(name string, public bool) error
+
+    // NamespaceSetLock set namespace in read-write protected or normal mode (0 or 1)
+	NamespaceSetLock(name string, lock bool) error
+
+    // DBSize returns the size of the database in bytes
+	DBSize() (uint64, error)
+}
+```
+