This loadtests the jwt decoding logic. For this it adds an optional
`-k`(kind) parameter to `postgrest-loadtest` and
`postgrest-loadtest-against`.
Old kind (default):
```
postgrest-loadtest -k mixed
postgrest-loadtest-against -k mixed
```
New kind:
```
postgrest-loadtest -k jwt
postgrest-loadtest-against -k jwt
```
Internally it uses a dynamically generated targets file using python
which looks like:
```
GET http://postgrest/authors_only
Authorization: Bearer <jwt>
GET http://postgrest/authors_only
Authorization: Bearer <another-jwt>
...
```
Then this is used to run vegeta with the `-lazy` option.
Timing dependent tests in the IO tests don't work too well when the next
commit increases the JWT parsing performance.
The remaining IO tests are for coverage and basic breakage. Loadtests
are adapted so that performance regressions for JWT caching would be
detected that way.
PR #2358 added a bulk insert to the loadtest. However this broke the regular insert test,
which just returned 400 Bad Request because of a missing PK value since. Adding the new
id column in the payload to the ?columns= argument fixes that.
steve-chavez