goroutine leak in driver package: init()

[crobert-1]

Context
See #130

Bug
Here's the goleak output:

[Goroutine 13 in state chan receive, with github.com/SAP/go-hdb/driver.(*metrics).collect on top of the stack:
github.com/SAP/go-hdb/driver.(*metrics).collect(0xc001a900a0, 0x0?, 0x0?)
        /Users/crobert/go/pkg/mod/github.com/!s!a!p/go-hdb@v1.7.1/driver/metrics.go:192 +0x97
created by github.com/SAP/go-hdb/driver.newMetrics in goroutine 1
        /Users/crobert/go/pkg/mod/github.com/!s!a!p/go-hdb@v1.7.1/driver/metrics.go:146 +0x510

This is caused by running a goroutine from within init. This leak will happen with every direct and indirect import of the driver package.

This is the line of code in init that will eventually start a running goroutine:

go-hdb/driver/driver.go

Line 40 in 36ea7b4

stdHdbDriver = &hdbDriver{metrics: newMetrics(nil, statsCfg.TimeUnit, statsCfg.TimeUpperBounds)}

Solution
I'd suggest only starting a goroutine when required by the package's functionality, and include a public way to stop it when execution is done.

[stfnmllr]

should be fixed with https://github.com/SAP/go-hdb/releases/tag/v1.7.5

[crobert-1]

Thanks @stfnmllr!