Linkcheck fails for valid URLs with `#<target>` part

[TibsAtWork]

https://github.com/aiven/devportal/pull/836 introduced two links into the Kafka documentation that fail at make linkcheck.

• https://kafka.apache.org/documentation/#consumerconfigs_auto.offset.reset
• https://kafka.apache.org/documentation/#design_consumerposition

Both of these definitely exist, and work in a browser.

For that PR, I've added explicit ignoring of those two links via linkcheck_ignore in the conf.py file.

This may or may not relate to https://github.com/sphinx-doc/sphinx/issues/9255 and/or the https://github.com/sphinx-doc/sphinx/issues/9016

Note: we also have devportal issue https://github.com/aiven/devportal/issues/631 which is perhaps fixed by upstream changes(https://github.com/sphinx-doc/sphinx/issues/9435) - I don't believe it's relevant here.