add ability to support free entry of environment variables for nango-server

[colinbjohnson]

This PR addresses Allow Arbitrary Environment Variables to be set for nango-server. I've attached a screenshot of a basicauth login below:

Note that there are a number of ways to support environment variables within helm charts - two options which I tested/considered are below:

1. Free-entry configuration - where a user would only provide an env value that renders valid YAML. This is rendered utilizing the following:

{{- if .Values.server.env }}
{{- toYaml .Values.server.env | nindent 12 }}
{{- end }}

2. Iterative configuration (which is what I've seen used more frequently) - where a user provides a list composed of name and value or valueFrom fields which (I thought) offered a greater deal of validation (see "A Note on Iterative Configuration" below).

A Note on Iterative Configuration

I was open to utilizing this as it was/is common within the kubernetes/helm community and a popular suggestion on AI sites. What I discovered was this was worse than simply accepting "free entry" as it modified the YAML but did not reject it - an example is below:

{{- range .Values.server.env }}
- name: {{ .name }}
  {{- if .value }}
  value: {{ .value | quote }}
  {{- else if .valueFrom }}
  valueFrom: {{ toYaml .valueFrom | nindent 16 }}
  {{- end }}
{{- end }}

When given:

env:
  - namea: FLAG_AUTH_ENABLED
    value: "false"
  - name: NANGO_DASHBOARD_USERNAME
    value: nango
  - name: NANGO_DASHBOARD_PASSWORD
    valueFroma:
      secretKeyRef:
        name: nango-secrets
        key: nango-dashboard-password

Would render:

- name: 
  value: "false"
- name: NANGO_DASHBOARD_USERNAME
  value: "nango"
- name: NANGO_DASHBOARD_PASSWORD

[khaliqgant]

Thanks!