Obtain OpenVDS build flags from pkg-config

If it is decided to use OpenVDS 3.0.4 or newer one could try using the [`pkg-config` support of CGO](https://pkg.go.dev/cmd/cgo#hdr-Using_cgo_with_the_go_command). This would automatically determine needed flags for compiling and linking code that uses OpenVDS.

Since 3.0.4 OpenVDS has a [pkg-config configuration file](https://community.opengroup.org/osdu/platform/domain-data-mgmt-services/seismic/open-vds/-/merge_requests/734). The OpenVDS project should know best what compile and link flags are needed to use their library.

This would affect

https://github.com/equinor/vds-slice/blob/5dec18ff75ad15d5c9be4c4e5643f24616d81c86/internal/vds/vds.go#L4-L5

which could be changed to

```go
#cgo pkg-config: openvds
```

This would imply that `pkg-config` is needed as dependency, but I am not sure if this dependency already exists in an implicit manner.