Dendrite auto publish (#1050)

- Created a package.json in servers/dendrite. Moving forward, this file
is our canonical dendrite version, and our docker builds will depend on
this version.
- Created a script that extracts the package.json version and puts it
into the GitHub actions build environment as `RELEASE_VERSION`.
- Updated the GitHub action so that it builds and publishes the docker
image to dockerhub whenever we merge dendrite changes to main.

Co-authored-by: Automated Version Bump <gh-action-bump-version@users.noreply.github.com>

get-version.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+# This script is used to extract the version string from the package.json file
+echo "$(cat package.json | grep version | head -1 | awk -F: '{ print $2 }' | sed 's/[",]//g' | tr -d '[[:space:]]')" 

package.json

@@ -0,0 +1,4 @@
+{
+  "name": "@herenotthere/dendrite-monolith",
+  "version": "1.0.34"
+}