Provide default job value (#15963)

This fixes the `helm template` warning when providing a job map.

```
warning: destination for jobs is a table. Ignoring non-table value <nil>
```

Signed-off-by: Hendrik Purmann <h.purmann@googlemail.com>

stable/jenkins/Chart.yaml

@@ -1,7 +1,7 @@
 apiVersion: v1
 name: jenkins
 home: https://jenkins.io/
-version: 1.4.1
+version: 1.4.2
 appVersion: lts
 description: Open source continuous integration server. It supports multiple SCM tools
   including CVS, Subversion and Git. It can execute Apache Ant and Apache Maven-based

stable/jenkins/README.md

@@ -138,7 +138,7 @@ The following tables list the configurable parameters of the Jenkins chart and t
 | `master.initScripts`              | List of Jenkins init scripts         | Not set                                   |
 | `master.credentialsXmlSecret`     | Kubernetes secret that contains a 'credentials.xml' file | Not set               |
 | `master.secretsFilesSecret`       | Kubernetes secret that contains 'secrets' files | Not set                        |
-| `master.jobs`                     | Jenkins XML job configs              | Not set                                   |
+| `master.jobs`                     | Jenkins XML job configs              | `{}`                                      |
 | `master.overwriteJobs`            | Replace jobs w/ ConfigMap on boot    | `false`                                   |
 | `master.installPlugins`           | List of Jenkins plugins to install. If you don't want to install plugins set it to `[]` | `kubernetes:1.14.0 workflow-aggregator:2.6 credentials-binding:1.17 git:3.9.1 workflow-job:2.31` |
 | `master.overwritePlugins`         | Overwrite installed plugins on start.| `false`                                   |

stable/jenkins/values.yaml

@@ -182,7 +182,7 @@ master:
   # master.key and hudson.util.Secret)
   # secretsFilesSecret: jenkins-secrets
   # Jenkins XML job configs to provision
-  jobs:
+  jobs: {}
   #  test: |-
   #    <<xml here>>