Twitter-oss: Prepare OSS libraries for release 21.3.0

Problem/Solution

Let's move the `dodo` CHANGELOG to RST so that it gets
updated on each release and prep the release for 21.3.0.

JIRA Issues: CSL-10793

Differential Revision: https://phabricator.twitter.biz/D641843

CHANGELOG.rst

@@ -7,6 +7,9 @@ Note that ``PHAB_ID=#`` and ``RB_ID=#`` correspond to associated messages in com
 Unreleased
 ----------
 
+21.3.0
+------
+
 Breaking API Changes
 ~~~~~~~~~~~~~~~~~~~~
 

README.md

@@ -1,6 +1,6 @@
 # TwitterServer
 
-[![Build Status](https://github.com/twitter/twitter-server/workflows/continuous%20integration/badge.svg?branch=develop)](https://github.com/twitter/twitter-server/actions?query=workflow%3A%22continuous+integration%22+branch%3Adevelop)
+[![Build Status](https://github.com/twitter/twitter-server/workflows/continuous%20integration/badge.svg?branch=release)](https://github.com/twitter/twitter-server/actions?query=workflow%3A%22continuous+integration%22+branch%3Arelease)
 [![Codecov](https://codecov.io/gh/twitter/twitter-server/branch/develop/graph/badge.svg)](https://codecov.io/gh/twitter/twitter-server)
 [![Project status](https://img.shields.io/badge/status-active-brightgreen.svg)](#status)
 [![Gitter](https://badges.gitter.im/twitter/finagle.svg)](https://gitter.im/twitter/finagle?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)

build.sbt

@@ -1,7 +1,7 @@
 import scoverage.ScoverageKeys
 
 // All Twitter library releases are date versioned as YY.MM.patch
-val releaseVersion = "21.3.0-SNAPSHOT"
+val releaseVersion = "21.3.0"
 
 val jacksonVersion = "2.11.2"
 val jacksonLibs = Seq(