Add go mod vendor to atc.dev.sh

[ericholguin]

Adds the go mod vendor command to the t3c run.sh file, for when a user has a clean repo t3c won't fail to start up due to missing packages

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Which Traffic Control components are affected by this PR?

• Dev CDN in a Box

What is the best way to verify this PR?

Have a clean repo or delete /vendor/golang.org/x/

cd dev/
source atc.dev.sh
atc build
atc start

Should find that t3c starts correctly and you will see /vendor/golang.org/x/ has been created and contains packages

PR submission checklist

• This PR has tests
• This PR has documentation
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

[zrhoffman]

The thing about adding go mod vendor to the t3c service is that the trafficops and trafficmonitor services also fail to build binaries and run i go mod vendor is not run for them.

So maybe the trafficops and trafficmonitor services could add a check to see if vendor/golang.org/x and vendor/modules.txt (which indicates that vendoring is complete) exist, and if not, wait until it does before continuing?

[zrhoffman]

If atc-build is run before docker-compose up, go mod vendor can be run in a container so the user doesn't need go (or the latest go version)

[ericholguin]

So run go mod vendor in the traffic ops Dockerfile?

[zrhoffman]

Nah, running go mod vendor from one of the docker-compose services using docker-compose run

[zrhoffman]

so, go mod vendor would go between docker-compose build and docker-compose up

[ericholguin]

Not sure I understand, but if you want to just add it to your open PR: #7142 I can close this and review that.