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/build/Dockerfile.buildenv

@@ -0,0 +1,3 @@
+FROM golang:1.19.5@sha256:bb9811fad43a7d6fd2173248d8331b2dcf5ac9af20976b1937ecd214c5b8c383
+
+RUN apt-get update && apt-get install -y make git apt-transport-https ca-certificates curl software-properties-common build-essential zip xmlsec1 jq