InfluxQL new syntax: FUTURE LIMIT and PAST LIMIT

[davidby-influx]

In the 1.x line (Enterprise and OSS), a new feature has been added which required changes to InfluxQL syntax.

There are two new reserved words, FUTURE and PAST, which are used in specifying write windows for retention periods.

Write windows prevent writes into a retention policy outside of optional future and past limits. These are specified as durations and are added and subtracted from now when determining a whether write is permitted, even if it is within the bounds of the retention policy.

If write limits are not specified, the default is current behavior (no write limits).
A write limit of 0 is treated is if there were no limit (this is how to remove a limit with an ALTER RETENTION statement)

Relevant URLs

influxdata/influxql#72
https://github.com/influxdata/plutonium/pull/4200
influxdata/influxdb#25424
influxdata/influxdb#25517
Somewhat outdated:
https://github.com/influxdata/plutonium/issues/3005
https://github.com/influxdata/feature-requests/issues/258
https://github.com/influxdata/feature-requests/issues/258

Will be released in
InfluxDB 1.12.0 OSS and Enterprise