[Endpoint] Adding image and fixing inputs

[jonathan-buttner]

This PR adds an image and some inputs so the kibana UI doesn't fail when installing the package.

[ruflin]

LGTM

I'm not covinced that the endpoint package will have to specify inputs in the end but it works for now.

[jonathan-buttner]

Thanks for the review, yeah I agree, I had to do this because the UI was throwing an error here: https://github.com/elastic/kibana/blob/master/x-pack/plugins/ingest_manager/public/applications/ingest_manager/sections/agent_config/create_datasource_page/step_configure_datasource.tsx#L188

@jfsiii @jen-huang I had to add this to the manifest:

    inputs:
      - type: metrics
      - type: events

https://github.com/elastic/package-registry/pull/260/files#diff-381ba165569ba08ab0eb43fc21b4cb66R22

otherwise the I think the UI was failing to find the packageInfo.datasources[0].inputs. Would it make sense to add inputs to the check as well?
Something like:
packageInfo.datasources && packageInfo.datasources[0] && packageInfo.datasources[0].input

[jen-huang]

@jonathan-buttner I'll add some additional safeguards here. Thanks!

[jen-huang]

PR that adds more null checks: elastic/kibana#60426

[jonathan-buttner]

Awesome thanks @jen-huang I'm testing it right now and then I'll 👍