Support for `expand` parameter

[pawcoding]

Motivation

Using expand allows you to specify additional properties to be included with API requests. This allows you to do database joins with one single request. Currently when you want to access data from multiple collections you need to configure two separate collections. While this is still the recommended way (especially for the classic build time loader), having this option for live loader allow for a reduced number of requests.

This was already requested in:

• Feature Request: add fields for custom filter and expand queries. #33
• Suggestion to be able to expand relational fields #39

Proposed Solution

A prototype for this already exists in:

• feat(expand): Enables the use of Pocketbases 'Expand' property #41

Since this is a very complex feature, I'd suggest to add experimental support for this in a multi step process. For this, I'll create a few sub-issues.

Alternatives Considered

As described above, you currently have to configure multiple collections for this to work.