Allow [runners.kubernetes.volumes] configuration in the helm chart

👋 We are continuing this discussion in #106 (closed), where we allow the user to specify any kind of configuration which would make this issue obsolute.

Description

A user can specify volumes when using the kubernetes execture. However when using the offical helm chart there is no possible option to set this up inside of values.yml

Proposal

When we reviewed !39 (closed) we found certain issues and came up with the following proposal:

• Allow user to specify config template gitlab-org/gitlab-runner!1263 (merged), this is required because right now all configuration was done through environment variables and things like volumes are not supported by environment variable since they are a complex structure.
• Start using config template for configuration generation !153 (closed)
• Update !39 (closed) to use the configuration template instead.

Other issues that it will solve

• #71 (closed)
• TLS configuration for DinD

Links to related issues and merge requests / references

!39 (closed)