gst-python: Add option to disable python plugin

It is not always needed, at least Ubuntu package it separately and don't
install it by default. Also when doing a static build there is an
unavoidable warning otherwise.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1337>

subprojects/gst-python/meson.build

@@ -97,11 +97,13 @@ if get_option('default_library') == 'shared'
 endif
 
 subdir('gi')
+if not get_option('plugin').disabled()
   if get_option('default_library') != 'static'
     subdir('plugin')
   else
     warning('Python plugin not supported with `static` builds yet.')
   endif
+endif
 if not get_option('tests').disabled()
   subdir('testsuite')
 endif

subprojects/gst-python/meson_options.txt

@@ -4,3 +4,4 @@ option('libpython-dir', type : 'string', value : '',
         description: 'Path to find libpythonXX.so')
 option('python', type : 'string', value : 'python3')
 option('tests', type : 'feature', value : 'auto', yield : true)
+option('plugin', type : 'feature', value : 'auto')