Create apicrud.rst

[sde1aney]

basic information around using POST operations for create, read, update, delete operations with the API. worked examples using the Trafficshaper API endpoint, curl syntax.

[AdSchellevis]

I don't mind extending the examples, but it should fit somewhere in the documentation. The most logic option is likely to add some common scenario's here https://docs.opnsense.org/development/how-tos/api.html

[sde1aney]

I'm happy for it to go wherever, I did put it as another how-to doc to avoid cluttering the existing API how-to page.
I had also considered putting a very small example on the trafficshaper page here https://docs.opnsense.org/development/api/core/trafficshaper.html, but decided it would then ideally require the equivalent examples on other pages.

[AdSchellevis]

a generic example using curl is probably better indeed.