devtools/config: add experiment config for e2e tests

The file e2e-config will be mounted into
the frontend docker container to toggle
experiments for e2e tests. The file is
mounted instead of copied so that experiments
can be changed without rebuilding the frontend
container.

Change-Id: I7ff0db94b760594e501af0b747cd766934081d1c
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/297555
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

devtools/config/docker-compose.yaml

@@ -46,6 +46,8 @@ services:
     image: pkgsite_frontend
     ports:
       - 8080:8080
+    volumes:
+      - './e2e-config.yaml:/app/experiment.yaml'
 
   migrate:
     depends_on:

devtools/config/e2e-config.yaml

@@ -0,0 +1,9 @@
+experiments:
+  - name: command-toc
+    rollout: 100
+  - name: directory-tree
+    rollout: 100
+  - name: interactive-playground
+    rollout: 100
+  - name: not-at-latest
+    rollout: 100