pgsql: SQL/JSON: Various improvements to SQL/JSON query function docs

SQL/JSON: Various improvements to SQL/JSON query function docs 1. Remove the keyword SELECT from the examples to be consistent with the examples of other JSON-related functions listed on the same page. 2. Add tags around the functions' syntax definition 3. Capitalize function names in the synta

pgsql: SQL/JSON: Various improvements to SQL/JSON query function docs

SQL/JSON: Various improvements to SQL/JSON query function docs 1. Remove the keyword SELECT from the examples to be consistent with the examples of other JSON-related functions listed on the same page. 2. Add tags around the functions' syntax definition 3. Capitalize function names in the synta