[collectd5] Default to use of RRASingle to keep rrd files small
[collectd] We want real ligcrypt support or removal
[collectd5] For mod-write-http use 1M buffer

We want to reduce the load on the server and 1M is not an unreasonable amount of memory to cache.  Therefore make the buffer for HTTP POST 1M on the assumption that if this results in too much latency we can do a FLUSH in order to force data out sufficiently frequently