Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/templates/partials/style.mjml

@@ -0,0 +1,11 @@
+<mj-attributes>
+  <mj-raw><link href="https://fonts.googleapis.com/css?family=Open+Sans:300,400,500,600,700" rel="stylesheet" type="text/css"></link></mj-raw>
+  <mj-text font-family="Open Sans, sans-serif" align="center" />
+  <mj-button font-family="Open Sans, sans-serif" background-color="#FFFFFF" border-radius="4px" padding="0px" />
+  <mj-image alt="" align="center" />
+  <mj-class name="email" align="center" padding="24px" background-color="#FFFFFF" border-radius="8px" />
+  <mj-class name="logo" width="132px" height="21.76px" padding="0px" />
+</mj-attributes>
+
+<mj-include type="css" path="./style.css"/>
+<mj-include type="css" css-inline="inline" path="./style.css"/>