bazel: Add container test for s3proxy (#62893)

* Add container test for s3proxy script

* Add explanatory comments

* Fixup s3proxy container structure test

* Update docs to mention a caveat of the setup steps

* Fix hostname

doc/dev/background-information/bazel/containers.md

@@ -138,6 +138,13 @@ commandTests:
       - -u
     excludedOutput: ["^0"]
     exitCode: 0
+
+  # Each command in the setup section will run in a separate container and then commits a modified image to be the new base image for the test run
+  - name: "fetch and test sg"
+    setup: [["wget", "https://github.com/sourcegraph/sg/releases/download/2024-05-23-19-04-d485d76e/sg_linux_amd64", "-O", "sg"], ["chmod", "+x", "sg"]]
+    command: "./sg"
+    args: ["--help"]
+    expectedOutput: ["The Sourcegraph developer tool"]
 ```
 
 We can now build this image _locally_ and run those tests as well.

docker-images/blobstore/s3_proxy_image_test.yaml

@@ -7,6 +7,15 @@ commandTests:
       - -u
     excludedOutput: ["^0"]
     exitCode: 0
+    # This test runs as a single command, as commands run in the setup block are not executed in the same container as the command block
+  - name: "s3proxy test"
+    command: "sh"
+    args: [
+      "-c",
+      "/opt/s3proxy/run-docker-container.sh >/dev/null 2>&1 & sleep 5 && curl -X PUT --write-out %{http_code} http://localhost:9000/create-bucket-test-2022-01-09-attempt0"
+    ]
+    expectedOutput: ["200"]
+    exitCode: 0
 
 fileExistenceTests:
 - name: 'Test for run-docker-container.sh'