SHOW MEASUREMENTS doesn't support time in WHERE clause

When running query

`SHOW MEASUREMENTS WITH MEASUREMENT=~/^mymsmt.*/ WHERE time>now()-1h`

I am getting error

'SHOW MEASUREMENTS doesn't support time in WHERE clause'

Documentation says that time filter is supported by SHOW MEASUREMENTS: [schema_exploration/#filter-meta-queries-by-time](https://docs.influxdata.com/influxdb/v1.7/query_language/schema_exploration/#filter-meta-queries-by-time)

> To filter other meta data, replace SHOW TAG KEYS with SHOW TAG VALUES, SHOW SERIES, SHOW MEASUREMENTS, SHOW FIELD KEYS, and so on.

It also mentions SHOW FIELD KEYS which doesn't even support WHERE clause!
This is inconsistency between implementation and documentation.

(I would prefer to have this implemented, as I was expecting it to exist and now seem to have to query each measurement for series in time range.)

InfluxDB v 1.7.10

Thank you very much.
Igor

Start by reproducing the SHOW MEASUREMENTS query with the time predicate and compare its behavior with the schema exploration documentation linked in the issue. Trace the schema meta-query handling to determine the supported WHERE clauses; done means the documented time filter works consistently, or the documentation accurately reflects the implementation.

Written by the indexing model from the issue text.