Custom Environment Variable Support

[jillianwilson]

This MR aims to address #152 . Because there are many possible environment variables that users may want to add to their helm chart was decided to add the option to include custom environment variables to be added to the connect, injector, and operator containers.

This work can be tested using the following steps:

1. Create a custom values file
2. Add the following text:

connect:
  customEnvVars:
    - name: "CUSTOM_ENV_VAR1"
      value: "customvar2"
    - name: "CUSTOM_ENV_VAR2"
      value: "customvar2"

3. Run the following command:

helm template -f newvalues.yaml connect ./connect

4. Check that the new environment variables have been added to the connect container in the manifest.
   These steps should be followed for the injector and operator containers as well.

[edif2008]

Functional review: ✅

I've tested the following cases and can confirm that all of them work as expected. 💪🏻

✅ Connect

helm template -f newvalues.yaml connect ./charts/connect > results.yaml

✅ Operator

helm template -f newvalues.yaml connect ./charts/connect --set connect.create=false --set operator.create=true > results.yaml

✅ Secrets Injector

helm template -f newvalues.yaml secrets-injector ./charts/secrets-injector > results.yaml

Code review: ✅

Code looks straight forward and on point.

Other notes

I've noticed the following warning when running the helm template commands:

$ helm template -f newvalues.yaml connect ./charts/connect > results.yaml
coalesce.go:286: warning: cannot overwrite table with non table for connect.connect.customEnvVars (map[])

I have a comment on the exact line that may be causing this, as well as a possible solution to it.