Remove fluent-style kingpin

[jkroepke]

This PR remove the fluent-style usage of kingpin by an dedicated instance of kingpin. This allow programs to embed windows_exporter and pass a customized kingpin instance to all collectors.

At the moment, its hard to embedded windows_exporter in an other application. While its possible to feed the kingpin.CommandLine instance outside from windows_exporter, there are conflicts with other exporters do the same.

PR tested in a Windows 10 client machine.

Example Code for injected collector configuration into the embedded windows_exporter instance:

// toExporterConfig converts integration Configs into windows_exporter configs.
func (c *Config) toExporterConfig(app *kingpin.Application) {
	app.GetFlag(collector.FlagDfsrEnabledCollectors).StringVar(&c.Dfsr.SourcesEnabled)
	app.GetFlag(collector.FlagExchangeCollectorsEnabled).StringVar(&c.Exchange.EnabledList)
	app.GetFlag(collector.FlagISSSiteBlacklist).StringVar(&c.IIS.SiteBlackList)
	app.GetFlag(collector.FlagISSSiteWhitelist).StringVar(&c.IIS.SiteWhiteList)
	app.GetFlag(collector.FlagISSAppBlacklist).StringVar(&c.IIS.AppBlackList)
	app.GetFlag(collector.FlagISSAppWhitelist).StringVar(&c.IIS.AppWhiteList)
	app.GetFlag(collector.FlagLogicalDiskVolumeBlacklist).StringVar(&c.LogicalDisk.BlackList)
	app.GetFlag(collector.FlagLogicalDiskVolumeWhitelist).StringVar(&c.LogicalDisk.WhiteList)
	app.GetFlag(collector.FlagMsmqWhereClause).StringVar(&c.MSMQ.Where)
	app.GetFlag(collector.FlagMssqlEnabledCollectors).StringVar(&c.MSSQL.EnabledClasses)
	app.GetFlag(collector.FlagNicBlacklist).StringVar(&c.Network.BlackList)
	app.GetFlag(collector.FlagNicWhitelist).StringVar(&c.Network.WhiteList)
	app.GetFlag(collector.FlagProcessBlacklist).StringVar(&c.Process.BlackList)
	app.GetFlag(collector.FlagProcessWhitelist).StringVar(&c.Process.WhiteList)
	app.GetFlag(collector.FlagScheduledTaskBlacklist).StringVar(&c.Process.BlackList)
	app.GetFlag(collector.FlagScheduledTaskWhitelist).StringVar(&c.Process.WhiteList)
	app.GetFlag(collector.FlagServiceWhereClause).StringVar(&c.Service.Where)
	app.GetFlag(collector.FlagServiceUseAPI).StringVar(&c.Service.UseApi)
	app.GetFlag(collector.FlagSmtpServerBlacklist).StringVar(&c.SMTP.BlackList)
	app.GetFlag(collector.FlagNicWhitelist).StringVar(&c.SMTP.WhiteList)
	app.GetFlag(collector.FlagTextFileDirectory).StringVar(&c.TextFile.TextFileDirectory)
}

[breed808]

Thanks for submitting this! I really like the code changes in this PR, it's very tidy and easy to follow 👍

[jkroepke]

That was fast! Thanks a lot @breed808 for merging this.