Doc: subdivide System Information Functions and Operators.
Provide <sect2> subdivisions in 9.26 System Information Functions and
Operators. This is useful because it adds a mini-TOC at the top of
the page to aid jumping to portions of what's become quite a long
section. Also, now that several of the subsections contain multiple
tables, it's hard to see the overall structure without headings.
Discussion: https://postgr.es/m/
4026789.
1670426602@sss.pgh.pa.us