[CI] Add container image for postsubmit testing of premerge config

This patch adds a container image and some necessary setup code so we can run
this through buildbot.

Pull Request: llvm#527

Author: boomanaiden154

premerge/buildbot/Dockerfile

@@ -0,0 +1,10 @@
+FROM ubuntu:24.04
+RUN apt-get update && apt-get install -y python3 python3-pip
+COPY requirements.lock.txt /requirements.lock.txt
+RUN pip3 install --break-system-packages -r /requirements.lock.txt && rm /requirements.lock.txt
+RUN mkdir /app
+WORKDIR /app
+COPY dispatch_job.py .
+COPY startup.sh .
+RUN chmod +x startup.sh
+ENTRYPOINT /app/startup.sh

premerge/buildbot/requirements.lock.txt

@@ -4,22 +4,46 @@
 #
 #    pip-compile --output-file=requirements.lock.txt requirements.txt
 #
+attrs==25.3.0
+    # via twisted
+autobahn==24.4.2
+    # via buildbot-worker
+automat==25.4.16
+    # via twisted
+buildbot-worker==3.11.7
+    # via -r requirements.txt
 cachetools==5.5.2
     # via google-auth
 certifi==2025.7.14
     # via
     #   kubernetes
     #   requests
+cffi==1.17.1
+    # via cryptography
 charset-normalizer==3.4.2
     # via requests
+constantly==23.10.4
+    # via twisted
+cryptography==45.0.5
+    # via autobahn
 durationpy==0.10
     # via kubernetes
 google-auth==2.40.3
     # via kubernetes
+hyperlink==21.0.0
+    # via
+    #   autobahn
+    #   twisted
 idna==3.10
-    # via requests
+    # via
+    #   hyperlink
+    #   requests
+incremental==24.7.2
+    # via twisted
 kubernetes==33.1.0
     # via -r requirements.txt
+msgpack==1.1.1
+    # via buildbot-worker
 oauthlib==3.3.1
     # via
     #   kubernetes
@@ -30,6 +54,8 @@ pyasn1==0.6.1
     #   rsa
 pyasn1-modules==0.4.2
     # via google-auth
+pycparser==2.22
+    # via cffi
 python-dateutil==2.9.0.post0
     # via kubernetes
 pyyaml==6.0.2
@@ -44,11 +70,23 @@ rsa==4.9.1
     # via google-auth
 six==1.17.0
     # via
+    #   buildbot-worker
     #   kubernetes
     #   python-dateutil
+twisted==25.5.0
+    # via buildbot-worker
+txaio==25.6.1
+    # via autobahn
+typing-extensions==4.14.1
+    # via twisted
 urllib3==2.5.0
     # via
     #   kubernetes
     #   requests
 websocket-client==1.8.0
     # via kubernetes
+zope-interface==7.2
+    # via twisted
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools

premerge/buildbot/requirements.txt

@@ -1 +1,2 @@
 kubernetes==33.1.0
+buildbot-worker==3.11.7

premerge/buildbot/startup.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+
+# This script performs all the necessary setup and then starts the buildbot
+# worker.
+
+mkdir /worker
+buildbot-worker create-worker /worker \
+  lab.llvm.org:9994 \
+  $BUILDBOT_USERNAME \
+  $BUILDBOT_PASSWORD
+
+echo "Google LLVM Premerge Infra Rotation <[email protected]>" \
+  > /worker/info/admin
+
+{
+  echo "Premerge container (https://github.com/llvm/llvm-project/pkgs/container/ci-ubuntu-24.04)"
+  echo "GCP n2/n2d standard instances."
+} > /worker/info/host
+
+buildbot-worker start /worker