Add support to preload content pack

[planetf1]

Add support to the Egeria-base chart to preload a specified content pack

In some cases the content pack may be already available on the server - by being in the assembly
Should also support dynamic download of a content pack from a specified URL.

Optional - We currently have 'downloads' added to development versions of our charts. I'm wondering about renaming this to 'connectors' or 'libraries' and adding a distinct entry. There's no technical necessity other than placing content packs and other ad hoc files within the library directory seems inappropriate.

cc: @mandy-chessell