Add headers configuration

What does it do

    Add headers configuration

    This is necessary so that our tests that set canary header can make use
    of installing the agent via Helm.

See for reference: gitlab-org/gitlab!104889 (comment 1183592865)

How to test

Having a file with custom values. Note the tag image with the minimum necessary commit to set up the config headers:

# test-file

config:
  headers:
    - "Cookie: gitlab-canary"
    - "Expires: Wed, 21 Oct 2015 07:28:00 GMT"
image:
  tag: fe716ea-race

Deploying the agent from the chart repo:

helm upgrade --install infra . \
    --namespace gitlab-agent \
    --create-namespace \
    --set image.tag=fe716ea \
    --set config.token=[REDACTED] \
    --set config.kasAddress=wss://kas.gitlab.com \
    -f test-file

Checking describe the pod and the pod logs in k9s: