Influxdb内存占用问题跟踪

This leak seems to have been introduced in 8aa224b,
present in 1.1.0 and 1.1.1.

When points were parsed from HTTP payloads, their tags and fields
referred to subslices of the request body; if any tag set introduced a
new series, then those tags then were stored in the in-memory series
index objects, preventing the HTTP body from being garbage collected. If
there were no new series in the payload, then the request body would be
garbage collected as usual.

Now, we clone the tags before we store them in the index. This is an
imperfect fix because the Point still holds references to the original
tags, and the Point's field iterator also refers to the payload buffer.
However, the current write code path does not retain references to the
Point or its fields; and this change will likely be obsoleted when TSI
is introduced.

This change likely fixes #7827, #7810, #7778, and perhaps others.