Document Jsonnet best practices

[simu]

As more people start writing Commodore components, questions regarding Jsonnet best practices are popping up more frequently.

While we already have #36 to document component architecture and interface principles and #40 to establish a Jsonnet style convention and guide, other best practice areas also need documentation, e.g.:

• best practices when using kube-libsonnet.

• Best practices for internal component structure, such as what belongs in a component library, when does it make sense to have multiple jsonnet files in component/, etc.

• Merging External Config Data

• Loops and Filters

• Component Library Functions

• Conditional Keys and Files

• Using kube-libsonnet

• Using Library functions

• CRD Group Versions

• Container Image & Helm Chart Versions

• Multiline Strings

• Component Structure

• Randomize (cron) schedules -> see Showcase how to randomize cron schedules #96

[srueg]

Draft PR with discussion notes: #86