fix: support complex extra env var map

[mgagliardo91]

There are currently two main ways to embed environment variables - extraEnvVars and extraEnvVarsMap. The former is a 1:1 mapping of the environment variable structure allowing for complex values (such as a value from a secret). The latter is a map of key/value where the value is only strings.

This PR allows the map method to support complex values.

The main reason for this is that you cannot combine lists via helm value merging functionality. Example:

# values.yaml

extraEnvVars:
  - name: A_VALUE
    value: "hello"
  - name: TEST
    value: "foo"

# values-prod.yaml
extraEnvVars:
  - name: TEST
    value: "bar"

When running helm template . -f values.yaml -f values-prod.yaml, the env var A_VALUE will be excluded as the merging of the two lists resolves by taking the latter in full, since this is no way to determine which overrides the other.

When using a map, however:

# values.yaml

extraEnvVarsMap:
  - A_VALUE: "hello"
  - TEST: "foo"

# values-prod.yaml
extraEnvVarsMap:
  - TEST: "bar"

The merged output will be:

extraEnvVarsMap:
  - A_VALUE: "hello"
  - TEST: "bar"

[mgagliardo91]

@skmannion example of/reason for usage: https://github.com/ndustrialio/nionic-api/pull/2578