[Feature Request] add thermal relief option for vias

Description

Currently, KiCad does not support adding thermal spokes (heat reliefs) to vias. This capability would be highly beneficial for high-density designs, particularly where via-in-pad is required.

Why is this useful

In dense LGA/BGA layouts, especially with pitch below 0.5 mm,via-in-pad routing is often necessary for signal fan-out. When these vias tie directly to ground or power planes, the resulting large thermal mass complicates soldering and rework, and makes part substitution more difficult.
Pads already offer configurable heat relief for copper zone connections; enabling the same functionality for vias would significantly improve testability and thermal behavior for via-in-pad vias for plane-connected nets.

Currently, the only workarounds are to either place keepout zones around vias and manually connect them to copper, or to modify footprints by replacing vias with pad objects configured with heat reliefs (either by modifying the local footprint or by creating custom footprints for the single pad). Both approaches are inefficient and error-prone.

KiCad Version

Application: KiCad PCB Editor x64 on x64

Version: 9.99.0-4185-gee9582b4ac, release build

Libraries:
	wxWidgets 3.3.1
	FreeType 2.13.3
	HarfBuzz 12.2.0
	FontConfig 2.15.0

Platform: Windows 10 (build 19045), 64-bit edition, 64 bit, Little endian, wxMSW
OpenGL: Intel, Intel(R) Iris(R) Xe Graphics, 4.6.0 - Build 32.0.101.7026

	wxWidgets: 3.3.1 (wchar_t,STL containers)
	Boost: 1.89.0
	OCC: 7.9.2
	Curl: 8.17.0-DEV
	ngspice: 45.2
	Compiler: Visual C++ 1944 without C++ ABI
	KICAD_IPC_API=ON
	KICAD_USE_PCH=OFF

Locale: 
	Lang: en_CH
	Enc: UTF-8
	Num: 1’234.5
	Encoded кΩ丈: D0BACEA9E4B888 (sys), D0BACEA9E4B888 (utf8)