Fix Rust Sample Docker image

[markmandel]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug

/kind cleanup
/kind documentation
/kind feature
/kind hotfix

What this PR does / Why we need it:

Looks like the Docker image and accompanying build scripts weren't updated with the move to Tonic, so it all went 💥.

This fixes that, removing lots of dependencies we no long need (yay Tonic), upgrading the Rust version, and making sure all the relevant code (e.g. protos) are copies to the appropriate place when creating the Docker build image.

Which issue(s) this PR fixes:

Work on #2179

Special notes for your reviewer:

[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

Note to project maintainer: There may be cases where the author cannot leave a comment, or the comment is not properly detected as consent. In those cases, you can manually confirm consent of the commit author(s), and set the cla label to yes (if enabled on your project).

ℹ️ Googlers: Go here for more info.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: markmandel, roberthbailey

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [markmandel,roberthbailey]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[agones-bot]

Build Succeeded 👏

Build Id: ea45c860-4fd1-496b-989b-008f394cddf0

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.16.0-0a1d3fc
• image: gcr.io/agones-images/agones-ping:1.16.0-0a1d3fc
• Linux C++ SDK (build): agonessdk-1.16.0-0a1d3fc-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.16.0-0a1d3fc.zip

A preview of the website (the last 30 builds are retained):

• https://0a1d3fc-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2180/head:pr_2180 && git checkout pr_2180
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.16.0-0a1d3fc