Improve the Replication section

Author: patiencedaur

doc/dev_guide/internals/iproto/images/repl_ballot.puml

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+@startuml
+
+skinparam map {
+    HyperlinkColor #0077FF
+    FontColor #313131
+    BorderColor #313131
+    BackgroundColor transparent
+}
+
+json "**IPROTO_BALLOT body**" as ballot {
+    "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_BALLOT_IS_RO_CFG]]": "MP_BOOL",
+    "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_BALLOT_VCLOCK]]": "MP_MAP",
+    "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_BALLOT_GC_VCLOCK]]": "MP_MAP",
+    "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_BALLOT_IS_RO]]": "MP_BOOL",
+    "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_BALLOT_IS_ANON]]": "MP_BOOL",
+    "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_BALLOT_IS_BOOTED]]": "MP_BOOL",
+    "(Optional) [[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_BALLOT_CAN_LEAD]]": "MP_BOOL"
+}
+
+@enduml

doc/dev_guide/internals/iproto/images/repl_ballot.svg

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+@startuml
+
+skinparam map {
+    HyperlinkColor #0077FF
+    FontColor #313131
+    BorderColor #313131
+    BackgroundColor transparent
+}
+
+json "**Heartbeat message from master**" as heartbeat_request {
+    "Size": "MP_UINT",
+    "Header": {
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_REQUEST_TYPE]]": "0",
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_REPLICA_ID]]": "2",
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_TIMESTAMP]]": "MP_DOUBLE"
+    }
+}
+
+json "**Response from replica**" as heartbeat_response {
+    "Size": "MP_UINT",
+    "Header": {
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_REQUEST_TYPE]]": "IPROTO_OK",
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_REPLICA_ID]]": "2"
+    },
+    "Body": {
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_VCLOCK]]": "{1, 6}"      
+    }
+}
+
+@enduml

doc/dev_guide/internals/iproto/images/repl_heartbeat.puml

@@ -0,0 +1,21 @@
+@startuml
+
+skinparam map {
+    HyperlinkColor #0077FF
+    FontColor #313131
+    BorderColor #313131
+    BackgroundColor transparent
+}
+
+json "**IPROTO_JOIN**" as join_request {
+    "Size": "MP_UINT",
+    "Header": {
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_REQUEST_TYPE]]": "IPROTO_JOIN",
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_SYNC]]": "MP_UINT"
+    },
+    "Body": {
+      "[[https://tarantool.io/en/doc/latest/dev_guide/internals/iproto/keys IPROTO_INSTANCE_UUID]]": "MP_UUID of this instance"
+    }
+}
+
+@enduml