Merge pull request #4258 from octo/6/write_redis

[collectd 6] feat: Port the write_redis plugin to collectd 6.

diff --cc src/collectd.conf.in
Simple merge

diff --cc src/collectd.conf.pod
Simple merge

diff --cc src/daemon/utils_cache.c
Simple merge

diff --cc src/utils/format_json/format_json_test.c
Simple merge