Add dgp related docs

Summary:
The following documents related to dynamic graph partitioning
are added:
  * Dependency Diagram
  * Feature Specification
  * Feature Reference

Reviewers: teon.banek

Reviewed By: teon.banek

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1584

docs/dev/diagram/dgp/logical.dot

@@ -0,0 +1,22 @@
+digraph {
+  // label="Dynamig Graph Partitioning";
+  fontname="Roboto Bold"; fontcolor=black;
+    fontsize=26; labelloc=top; labeljust=center;
+  compound=true; // If true, allow edges between clusters
+  rankdir=TB; // Alternatives: LR
+  node [shape=record fontname="Roboto", fontsize=12, fontcolor=white
+        style=filled, color="#FB6E00" fillcolor="#FB6E00"];
+  edge [color="#B5AFB7"];
+
+  "distributed::DistributedGraphDb" -> "distributed::TokenSharingRpcServer";
+
+  "distributed::TokenSharingRpcServer" -> "communication::rpc::Server";
+  "distributed::TokenSharingRpcServer" -> "distributed::Coordination";
+  "distributed::TokenSharingRpcServer" -> "distributed::TokenSharingRpcClients";
+  "distributed::TokenSharingRpcServer" -> "storage::dgp::Partitioner";
+
+  "storage::dgp::Partitioner" -> "distributed::DistributedGraphDb" [style=dashed];
+
+  "storage::dgp::Partitioner" -> "storage::dgp::VertexMigrator";
+  "storage::dgp::VertexMigrator" -> "database::GraphDbAccessor" [style=dashed];
+}

docs/feature_ref/dynamic_graph_partitioning.md

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+## Dynamic Graph Partitioner
+
+Memgraph supports dynamic graph partitioning which dynamically improves
+performance on badly partitioned dataset over workers. To enable it, the user
+should use the following flag when firing up the *master* node:
+
+```plaintext
+--dynamic_graph_partitioner_enable
+```
+
+### Parameters
+
+| Name | Default Value | Description | Range |
+|------|---------------|-------------|-------|
+|--dgp_improvement_threshold | 10 | How much better should specific node score
+be to consider a migration to another worker. This represents the minimal
+difference between new score that the vertex will have when migrated and the
+old one such that it's migrated. | Min: 1, Max: 100
+|--dgp_max_batch_size | 2000 | Maximal amount of vertices which should be
+migrated in one dynamic graph partitioner step. | Min: 1, Max: MaxInt32 |