Feature assemblies base

[webdevinition]

Hello @jbtronics,

In relation to https://github.com/Part-DB/Part-DB-server/pull/1051 the feature for adding the base of assembly as an new data source. Also mentioned in the discussion under https://github.com/Part-DB/Part-DB-server/discussions/1041, section 1.

The changes are the remaining delta to the other extracted feature pull requests related to the mentioned discussion.

Configuration opportunity of Bills of Materials (BOMs) with referencing of other assemblies, cycle prevention included

Simplified import overview with template description for filling the parts lists (BOM) of an assembly

Human-readable export in CSV and PDF format for simplified viewing of basic information

Human-readable export in PDF format to simplify understanding of which parts are actually required for a multiply nested assembly, for example, completely independent of a build function as is the case with projects.

Thanks for everything so far! I am grateful for integration!

Best regards, Marcel