Rich querying API for content collections

[snimavat]

Body

Summary

Currently the Astro content support is based on getCollection() and getEntryBySlug()

This is good enough for most use cases, however it lacks rich query API.
Some similar frameworks such as NuxtJS Content module provides rich set of API for querying content.

Background & Motivation

Lack of rich set of querying API forces developers to implement it their self.
Other similar frameworks are available which provides excellent querying capabilities for markdown content.

It will help developers implement complex, nested content organisation, and flexibility to query and display
based on different criteria effectively and without code duplication.

Goals

• Capability to query by different fields of front matter
• Capability to query certain fields only instead of whole glob
• capability to query just single, or multiple documents
• Capability to use max, limit, offset for queries returning list of content entries
• Support for basic. criterias, such as '$eq', '$gt' '$lt', '$in' etc

Example

• queryContent('articles').where({ title: 'Home' }).findOne()
• const articles = await queryContent('articles').where({ name: { $in: ['odin', 'thor'] } }).find()
• queryContent('articles').skip(5).limit(5).find()
• queryContent('articles').only('id').find()

[matthewp]

Thanks for submitting. This is something we are very interested in supporting, as we have seen the limits that come with attempting to solve every use-case with specific APIs. The exact shape is unknown, but this is something we are likely working on as we approach 3.0.

[stereobooster]

Related: #689
For inspiration: https://github.com/blacksmithgu/obsidian-dataview