New docs: minimal docs for modules that lack them

[rnorth]

Improvement for the new mkdocs-based documentation.

I'd expect that this doesn't need to be done in one big PR; it could be several.

We need some basic docs and examples (pulled in using the codeinclude macro) for:

• docs/modules/mockserver.md
• docs/modules/nginx.md
• docs/modules/pulsar.md

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If you believe this is a mistake, please reply to this comment to keep it open. If there isn't one already, a PR to fix or at least reproduce the problem in a test case will always help us get back on track to tackle this.

[rnorth]

Looks like the following modules still lack any kind of documentation, which is quite sad:

• pulsar
• rabbitmq

and JDBC modules (which could be viewed as 'inheriting' some docs, so aren't really a big deal):

• cockroachdb
• clickhouse
• mysql
• postgres