Adds a cat api endpoint: /_cat/templates and its more specific version, /_cat/templates/{name}.
It looks something like:
$ curl "localhost:9200/_cat/templates?v"
name template order version
sushi_california_roll *avocado* 1 1
pizza_hawaiian *pineapples* 1
pizza_pepperoni *pepperoni* 1
The specified version (only allows * globs) looks like:
$ curl "localhost:9200/_cat/templates/pizza*"
name template order version
pizza_hawaiian *pineapples* 1
pizza_pepperoni *pepperoni* 1
Partially specified columns:
$ curl "localhost:9200/_cat/templates/pizza*?v=true&h=name,template"
name template
pizza_hawaiian *pineapples*
pizza_pepperoni *pepperoni*
The help text:
$ curl "localhost:9200/_cat/templates/pizza*?help"
name | n | template name
template | t | template pattern string
order | o | template application order number
version | v | version
Closes#20467
Alexander Lin