internal/perf: add "|" to InfluxDB allowed-in-string chars

Some of the new benchmarks have excessively creative
names.  The characters added to the regexp were observed
in actual benchmark names and the queries flowed to Influxdb
and it did not crash (and it returned what was expected),
so apparently they are okay.

For example, the originally offending query string was

`AllShortest/DijkstraAllPaths_AllBetween_1000×16|0.1(828)-96`

and the header on the (fixed) benchmark chart for it was

`AllShortest/DijkstraAllPaths_AllBetween_1000×16|0.1(828)-96`

so nothing was lost in translation.

(Note the "×" which is NOT "x", yay Unicode)

Change-Id: I5ec54e31a07cd8172e990d3728ee685c322a2d49
Reviewed-on: https://go-review.googlesource.com/c/build/+/816580
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

internal/perf/dashboard.go

diff --git a/internal/perf/dashboard.go b/internal/perf/dashboard.go
index c27a457..06e9b35 100644
--- a/internal/perf/dashboard.go
+++ b/internal/perf/dashboard.go
@@ -152,7 +152,7 @@
 
 // validateRe is an allowlist of characters for a Flux string literal. The
 // string will be quoted, so we must not allow ending the quote sequence.
-var validateRe = regexp.MustCompile(`^[a-zA-Z0-9(),=/_:;.-]+$`)
+var validateRe = regexp.MustCompile(`^[a-zA-Z0-9(),=/_:;.|×%*-]+$`)
 
 func validateFluxString(s string) error {
 	if !validateRe.MatchString(s) {