New CLI Flag --devel To Include Development/Prerelease Versions of Charts (#139)

* Include devel Flag for Toggling Dev Chart Versions

The flag `--devel` for enabling/disabling dev versions
of charts in following endpoints:
1. /api/helm/repositories/kafka-operator
2. /api/helm/repositories/versions
3. /api/helm/repositories/latestver

Signed-off-by: Bhargav Ravuri <bhargav.ravuri@infracloud.io>

* Run Tests on Devel Flag Related Changes

Signed-off-by: Bhargav Ravuri <bhargav.ravuri@infracloud.io>

---------

Signed-off-by: Bhargav Ravuri <bhargav.ravuri@infracloud.io>

pkg/dashboard/objects/testdata/repositories-invalid-cache-file.yaml

@@ -0,0 +1,6 @@
+apiVersion: ""
+generated: "0001-01-01T00:00:00Z"
+repositories:
+- cache: non-existing-index.yaml
+  name: non-existing
+  url: http://example.com/charts

pkg/dashboard/objects/testdata/repositories-malformed-manifest.yaml

@@ -0,0 +1,12 @@
+apiVersion: ""
+generated: "0001-01-01T00:00:00Z"
+- repositories:
+- caFile: ""
+  certFile: ""
+  insecure_skip_tls_verify: false
+  keyFile: ""
+  name: charts
+  pass_credentials_all: false
+  password: ""
+  url: https://charts.helm.sh/stable
+  username: ""

pkg/dashboard/objects/testdata/testing-index.yaml

@@ -64,3 +64,37 @@ entries:
           email: containers@bitnami.com
       icon: ""
       apiVersion: v2
+  traefik:
+    - apiVersion: v1
+      appVersion: 1.7.26
+      deprecated: true
+      description: A Traefik based Kubernetes ingress controller with Let's
+        Encrypt support
+      home: https://traefik.io/
+      icon: https://docs.traefik.io/assets/img/traefik.logo.png
+      keywords:
+      - traefik
+      - ingress
+      - acme
+      - letsencrypt
+      name: traefik
+      sources:
+      - https://github.com/containous/traefik
+      - https://github.com/helm/charts/tree/master/stable/traefik
+      version: 1.87.7-rc1
+  rabbitmq:
+    - apiVersion: v1
+      appVersion: 3.8.2
+      deprecated: true
+      description: DEPRECATED Open source message broker software that implements the Advanced
+        Message Queuing Protocol (AMQP)
+      home: https://www.rabbitmq.com
+      icon: https://bitnami.com/assets/stacks/rabbitmq/img/rabbitmq-stack-220x234.png
+      keywords:
+      - rabbitmq
+      - message queue
+      - AMQP
+      name: rabbitmq
+      sources:
+      - https://github.com/bitnami/bitnami-docker-rabbitmq
+      version: invalid-version