This adds support for using regex expressions in SHOW TAG VALUES when
selecting the key. Also supporting the `!=` operation for the
comparison. Now you can do any of the following:
SHOW TAG VALUES WITH KEY != "region"
SHOW TAG VALUES WITH KEY =~ /region/
SHOW TAG VALUES WITH KEY !~ /region/
It also adds a new SetLiteral AST node that will potentially be used in
the future to allow set operations for other comparisons in the future.
Fixes#4532.
`SHOW TAG VALUES` output has been modified to print the measurement name
for every measurement and to return the output in two columns: key and
value. An example output might be:
> SHOW TAG VALUES WITH KEY IN (host, region)
name: cpu
---------
key value
host server01
region useast
name: mem
---------
key value
host server02
region useast
`measurementsByExpr` has been taught how to handle reserved keys (ones
with an underscore at the beginning) to allow reusing that function and
skipping over expressions that don't matter to the call.
Fixes#5593.
Jonathan A. Sternberg
lvheyang
Ben Johnson