Enhance Kibana Reporting Settings - Exported PDF format templating features

[greicefaustino]

Describe the feature:

Add more options for setting up PDF format. Currently the only available option is:

xpackReporting:customPdfLogo (https://www.elastic.co/guide/en/kibana/current/advanced-options.html#kibana-reporting-settings)

Describe a specific use case for the feature:

Examples of useful options:

• page formatting (e.g. margin sizes, page colour or backgrounds, content in header and footer)
• control over in which order are widgets added on each page
• replicate how widgets are set in the dashboard (maintaining proportion, if possible, but keep a similar distribution to what is seen on screen).

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)