Support OpenSLO v1

[luisdavim]

I have a openslo/v1 spec file that is valid:

$ oslo validate -f ./hung_operations.yaml
Valid!

but sloth can't read it:

$ sloth generate -i hung_operations.yaml
INFO[0000] SLI plugins loaded                            plugins=0 svc=storage.FileSLIPlugin version=0.12.0 window=30d
INFO[0000] SLO period windows loaded                     svc=alert.WindowsRepo version=0.12.0 window=30d windows=2
error: "generate" command failed: invalid spec, could not load with any of the supported spec types%

[snapydziuba]

Because Sloth currently only supports the v1alpha

sloth/pkg/common/model/slo_prometheus.go

Line 72 in ff0dced

OpenSLOV1Alpha *openslov1alpha.SLO

https://sloth.dev/examples/openslo/getting-started/

[luisdavim]

Right, this issue is to request support for v1 to be added.