Add a script to allow more users to easily upload artifacts

This makes it so that anyone with access to buildkite can upload an
artifact to the build server. Existing protections entail:
1. Doesn't allow users to run this against anything other than the
   master branch.
2. Does not allow overwriting existing files.
3. Does not touch files outside of the
   /data/files/frc971/Build-Dependencies/ directory.

Certainly no riskier than our regular CI at this stage.

This does cause a surprising amount of disk usage on the software971
server, due to bazel it extracting the amd64 toolchains.

Steps required to get this set up were:
1. Install the buildkite-agent apt package.
2. Configure the token in /buildkite/buildkite-agent.cfg, and set
   queue=deploy.
3. Start the buildkite-agent service.
4. Add the buildkite-agent user to the www-data group.
5. Add a new gerrit public key for the buildkite user corresponding to
   the new agent.
6. Set up the https://buildkite.com/spartan-robotics/deploy-artifact
   pipeline.

Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
Change-Id: I89416d23e8d75102314c7aa1dbe8b9fd64f4f762
diff --git a/tools/python/requirements.txt b/tools/python/requirements.txt
index 3b3ab3a..0a5f24a 100644
--- a/tools/python/requirements.txt
+++ b/tools/python/requirements.txt
@@ -12,6 +12,7 @@
 requests
 scipy
 shapely
+validators
 yapf
 
 # TODO(phil): Migrate to absl-py. These are abandoned as far as I can tell.