Adding certificats to runner

Adding specific certificats like self-signed certificats https://docs.gitlab.com/runner/configuration/tls-self-signed.html#supported-options-for-self-signed-certificates-targeting-the-gitlab-server

in /home/gitlab-runner/.gitlab-runner/certs/

Based on kubernetes secret object.

see helm chart reference: certsSecretName

## Set the certsSecretName in order to pass custom certficates for GitLab Runner to use
## Provide resource name for a Kubernetes Secret Object in the same namespace,
## this is used to populate the /home/gitlab-runner/.gitlab-runner/certs/ directory