OTLPLog Exporter Should Not Percent Decode Header Keys When Parsing Headers

[zhihali]

This issue originally from #5623. And as the PR review suggest, should implement a fix in otlplog as well.

We need to do the same for otlplog.

opentelemetry-go/exporters/otlp/otlplog/otlploghttp/config.go

Lines 551 to 556 in 772d3d7

	escKey, e := url.PathUnescape(rawKey)
	if e != nil {
	err = errors.Join(err, fmt.Errorf("invalid header key: %s", rawKey))
	continue
	}
	key := strings.TrimSpace(escKey)

Originally posted by @dmathieu in #5705 (review)

and I'll implement a fix later

[pellared]

It is a duplicate of #5623.