docs(query-builder): update topic with nested queries and templating

[igdmdimitrov]

Closes #5953

Checklist:

• check topic's TOC/menu and paragraph headings
• Include TOC topic labels in topic content has a valuable update, it's new or considered as preview\ beta
• link to other topics using ../relative/path.md
• at the References section at the end of the topic add links to topics, samples, etc
• reference API documentation instead of adding a section with API

• use valid component names - [Data] Grid, IgxSelectComponent, <igx-combo>
• use spell checker tool (VS Code, Grammarly, Microsoft Editor)
• add inline code blocks for the names of classes / tags / properties
• add language descriptor for the code blocks
• check broken links (use browser add-on)
• check if sample is working and fully visible in the topic
• check if sample is working and fully visible in the StackBlitz
• check if code blocks match the code in StackBlitz demo

• follow SEO guidelines to fill topic's metadata (SEO guidelines)

• do not resolve requested changes (leave that to the reviewer)
• add pending-localization label when the review of the PR is done
• add a member from the localization team to translate it

[gedinakova]

I suggest we use an IgxSelectComponent as we decided the sample to use it.

[igdmdimitrov]

Yes, this snippet will be updated once we have a templating sample ready.

[Otixa]

Left a very minor suggestion. Looks good otherwise! 👍