Add Synapse version deploy annotations to Grafana dashboard (#15674)

Fix https://github.com/matrix-org/synapse/issues/15662

This manifests as purple lines that show up on all time series panels
that you can hover and see what version was deployed.

Also added a new "Deployed Synapse versions over time" panel
where the color block changes with each version. And mixed this
color block into the "Up" time series panel.

To get the Grafana dashboard JSON to copy here: use the **Share** icon at the top -> **Export** -> check the **Export for sharing externally** option -> **View JSON** or **Save to file**

changelog.d/15674.feature

@@ -0,0 +1 @@
+Add Syanpse version deploy annotations to Grafana dashboard which enables easy correlation between behavior changes witnessed in a graph to a certain Synapse version and nail down regressions.