document errands support in reference dataset

[gberche-orange]

Expected behavior

https://github.com/orange-cloudfoundry/cf-ops-automation/blob/develop/docs/reference_dataset/template_repository/hello-world-root-depls/bosh-deployment-sample/deployment-dependencies.yml should illustrate usage of the errand

Observed behavior

errand support is documented into https://github.com/orange-cloudfoundry/cf-ops-automation#bosh-deployment-resources-template-format

to generate an additional errand step, in a deployment-dependencies.yml file, insert a key errands with a subkey named like the errand job to execute

Affected release

Reproduced on version 3.0

[o-orand]

Indeed as we use ngnix bosh release, we're not able to illustrate errand feature with a running example. We can try to add shield bosh release (@JCL38-ORANGE suggestion). Or we try to find another simple boshrelease with less dependencies with errand.
I think we should not replace ngnix, but rather add a new deployment in HelloWorldRootDeployment to illustrate 'errand'. BoshSampleDeployment starts to be huge and quite complex.

[o-orand]

Zookeeper seems to be a good candidate to use a sample or Generic-scripting-release once published on bosh.io