add meson option to build only the library

[rursprung]

Is your feature request related to a problem? Please describe.
as per the README it should be possible to build only the library:

aravis/README.md

Lines 48 to 49 in bf96964

	It is perfectly possible to only build the library, reducing the dependencies to
	the bare minimum.

and while it's possible to pass -Dviewer=disabled -Dgst-plugin=disabled it still builds arv-tool & co. because this is done unconditionally:

aravis/src/meson.build

Lines 322 to 336 in bf96964

	progs = [
	[ 'arv-tool', 'arvtool.c'],
	[ 'arv-test', ['arvtest.c'] + arv_test_resources],
	[ 'arv-camera-test', 'arvcameratest.c'],
	[ 'arv-fake-gv-camera', 'arvfakegvcamera.c'],
	]
	foreach p: progs
	executable ((p[0] + '-@0@').format (aravis_api_version),
	p[1],
	link_with: aravis_library,
	c_args: library_c_args,
	dependencies: aravis_dependencies,
	install: true)
	endforeach

Describe the solution you'd like
a new config option is introduced to suppress the build of executables (probably should be a default-enabled option build-tools or similar or maybe even one option per tool?)

Describe alternatives you've considered
n/a

Additional context
i noticed this while packaging up aravis for vcpkg (where it's only used as a library dependency of other things, so no binaries should be built/installed): microsoft/vcpkg#42351

in vcpkg the CI fails because it expects that there are no executables present. it'd be great if this could be added here as a config option, alternatively i'll have to provide a patch in vcpkg which will remove this part of the meson build (it'd be better to have it here upstream rather than having a downstream patch)