move upgrade process graph to the release-specific page

The graphic is now really out of date and not really useful anymore:
it shows that we are basically finished, but that we're also dragging
old machines around for quite a while.

We need to build a new dataset for bullseye now, and it doesn't make
much sense to keep all that old data around anyways.

howto/upgrades.md

@@ -9,17 +9,6 @@ major release. Here are the currently documented ones:
 
  * [buster](howto/upgrades/buster)
 
-<figure>
-<img alt="graph showing planned completion date, currently around july 2020" src="/howto/upgrades/predict-stretch.png" />
-<figcaption>
-
-The above graphic shows the progress of the migration between major
-releases. It can be regenerated with the [predict-os](https://gitlab.com/anarcat/predict-os) script. It
-pulls information from [howto/puppet](howto/puppet) to update a [CSV file](data.csv) to
-keep track of progress over time.
-</figcaption>
-</figure>
-
 ### Team-specific upgrade policies
 
 Before we perform a major upgrade, it might be advisable to consult

howto/upgrades/buster.md

@@ -338,3 +338,15 @@ List of servers to upgrade can be obtained with:
     $ curl -s -G http://localhost:8080/pdb/query/v4 --data-urlencode 'query=nodes { facts { name = "lsbdistcodename" and value = "stretch" }}' | jq .[].certname | sort
 
 Policy established in [howto/upgrades](howto/upgrades).
+
+<figure>
+<img alt="graph showing planned completion date, currently around September 2020" src="/howto/upgrades/buster/predict.png" />
+<figcaption>
+
+The above graphic shows the progress of the migration between major
+releases. It can be regenerated with the [predict-os](https://gitlab.com/anarcat/predict-os) script. It
+pulls information from [howto/puppet](howto/puppet) to update a [CSV file](data.csv) to
+keep track of progress over time.
+</figcaption>
+</figure>
+

howto/upgrades/Makefile → howto/upgrades/buster/Makefile

 # source for this program is https://gitlab.com/anarcat/predict-os
 PROG=predict-os
 
-predict-stretch.png: data.csv
-	$(PROG) predict graph -o
+predict.png: data.csv
+	$(PROG) predict graph -o $@ --path $>
 
 data.csv: FORCE
 	$(PROG) refresh