Export Drawing Sheet keywords ${author} and ${subject} to PDF plot properties

Description

Currently: ${TITLE} Drawing Sheet property is exported to PDF plot properties. Desired: ${AUTHOR} and ${SUBJECT} keywords added to Drawing Sheet and Page Settings dialog. Exports to PDF properties.

Steps to reproduce

KiCad Version

Application: KiCad x64 on x64

Version: 8.0.0, release build

Libraries:
	wxWidgets 3.2.4
	FreeType 2.12.1
	HarfBuzz 8.3.0
	FontConfig 2.14.2

Platform: Windows 10 (build 19045), 64-bit edition, 64 bit, Little endian, wxMSW

	wxWidgets: 3.2.4 (wchar_t,wx containers)
	Boost: 1.83.0
	OCC: 7.7.1
	Curl: 8.5.0-DEV
	ngspice: 42
	Compiler: Visual C++ 1936 without C++ ABI

Build settings: