The term `parameter` is a better word than `argument` for data passed
to an API endpoint; this is why OpenAPI uses in their terminology.
Replace `argument` with `parameter` in the API docs to improve their
readability.
Fixes#15435.
Firstly, change endpoint descriptions in zulip.yaml so that they
match their counterpart in the api docs. Then edit the api docs
so that they use api description markdown extension for displaying
endpoint description.
Openapi had descriptive response codes for endpoints with multiple
responses for same response code. But this does not fall in line
with openapi specifications. So change descriptive response codes
like "400_auth" and "400_anauth" to "400_0" and "400_1" for all
such endpoints. Also make the necessary changes in openapi.py so
as to be able to read the schema in such cases and generate example
in such cases.
The previous code for the validator test was fairly messy due to
checking for both formats of the openapi url, one with
<variable_name> and the other with {variable_name}. To eliminate
this, we have standardized the format and restricted it to
{variable_name} as per the official format at:
https://swagger.io/docs/specification/describing-parameters.