fix: enforce yaml config #63

[raffis]

Current situation

Currently the exporter requires a .yaml suffix for the config file, otherwise it fails to start:

panic: Unsupported Config Type ""

goroutine 1 [running]:
github.com/raffis/mongodb-query-exporter/cmd.initConfig()
	/home/raffi/mongodb-query-exporter/cmd/root.go:169 +0x125
github.com/spf13/cobra.(*Command).preRun(...)
	/home/raffi/.gvm/pkgsets/go1.18/global/pkg/mod/github.com/spf13/cobra@v1.6.1/command.go:946
github.com/spf13/cobra.(*Command).execute(0x12ab340, {0xc000032190, 0x2, 0x2})
	/home/raffi/.gvm/pkgsets/go1.18/global/pkg/mod/github.com/spf13/cobra@v1.6.1/command.go:876 +0x563
github.com/spf13/cobra.(*Command).ExecuteC(0x12ab340)
	/home/raffi/.gvm/pkgsets/go1.18/global/pkg/mod/github.com/spf13/cobra@v1.6.1/command.go:1044 +0x3bc
github.com/spf13/cobra.(*Command).Execute(...)
	/home/raffi/.gvm/pkgsets/go1.18/global/pkg/mod/github.com/spf13/cobra@v1.6.1/command.go:968
github.com/raffis/mongodb-query-exporter/cmd.Execute(...)
	/home/raffi/mongodb-query-exporter/cmd/root.go:118
main.main()
	/home/raffi/mongodb-query-exporter/main.go:8 +0x25
exit status 2

Proposal

Config type is now always yaml no matter the file suffix given.