DOC: Move multiple yaxis example from Spines to Subplots, axes and figures

The primary aspect here is the multiple Axis feature. Therefore it should live next to the other `twinx()` examples. The spine aspect is only a technical detail need to move the third y-axis. A user would not look for this in the Spines section.

Author: timhoffm

galleries/examples/subplots_axes_and_figures/multiple_yaxis_with_spines.py

@@ -46,3 +46,6 @@
 ax.legend(handles=[p1, p2, p3])
 
 plt.show()
+
+# %%
+# .. tags:: component: spines