Meson: Set some options back to auto by default

Some options got enabled by default since that commit:
gstreamer/gstreamer@40371ff9

While the commit message example makes perfect sense to enable `bad` by
default, I don't think the same reasoning applies to libav, devtools,
ges and rtsp_server.

I think it is important to keep a build with `-Dauto_features=disabled`
minimal, especially not pulling external dependencies. For example, with
libav being enabled by default, Meson builds FFmpeg subproject even
when disabling auto features.

It is fine to keep `bad` enabled by default because itself has auto
features for every plugins, when auto features are disabled it only
build libraries that does not have external deps.

Part-of: <gstreamer/gstreamer!5337>

meson_options.txt

@@ -3,10 +3,10 @@ option('base', type : 'feature', value : 'enabled')
 option('good', type : 'feature', value : 'enabled')
 option('ugly', type : 'feature', value : 'enabled')
 option('bad', type : 'feature', value : 'enabled')
-option('libav', type : 'feature', value : 'enabled')
-option('devtools', type : 'feature', value : 'enabled')
-option('ges', type : 'feature', value : 'enabled')
-option('rtsp_server', type : 'feature', value : 'enabled')
+option('libav', type : 'feature', value : 'auto')
+option('devtools', type : 'feature', value : 'auto')
+option('ges', type : 'feature', value : 'auto')
+option('rtsp_server', type : 'feature', value : 'auto')
 option('rs', type : 'feature', value : 'disabled')
 option('vaapi', type : 'feature', value : 'disabled')
 option('gst-examples', type : 'feature', value : 'auto', description : 'Build gst-examples subproject')