add hybrid 3d box level plot

Plots doesn't support level argument for 3d box. It may be good to add.

This examples gives an error "must specify coordinate axis slice for 3D hybrid plots".
```
FT = Float64
xelem = 10
yelem = 5
velem = 40
npoly = 4

vertdomain = ClimaCore.Domains.IntervalDomain(
ClimaCore.Geometry.ZPoint{FT}(0),
ClimaCore.Geometry.ZPoint{FT}(1000);
boundary_tags = (:bottom, :top),
)
vertmesh = ClimaCore.Meshes.IntervalMesh(vertdomain, nelems = velem)
vert_center_space = ClimaCore.Spaces.CenterFiniteDifferenceSpace(vertmesh)

xdomain = ClimaCore.Domains.IntervalDomain(
ClimaCore.Geometry.XPoint{FT}(-500) ..
ClimaCore.Geometry.XPoint{FT}(500),
periodic = true,
)
ydomain = ClimaCore.Domains.IntervalDomain(
ClimaCore.Geometry.YPoint{FT}(-100) ..
ClimaCore.Geometry.YPoint{FT}(100),
periodic = true,
)

horzdomain = ClimaCore.Domains.RectangleDomain(xdomain, ydomain)
horzmesh = ClimaCore.Meshes.RectilinearMesh(horzdomain, xelem, yelem)
horztopology = ClimaCore.Topologies.Topology2D(horzmesh)

quad = ClimaCore.Spaces.Quadratures.GLL{npoly + 1}()
horzspace = ClimaCore.Spaces.SpectralElementSpace2D(horztopology, quad)

hv_center_space = ClimaCore.Spaces.ExtrudedFiniteDifferenceSpace(
horzspace,
vert_center_space,
)

coords = ClimaCore.Fields.coordinate_field(hv_center_space)
Plots.plot(coords.x, level=3)
```

`Plots.plot(level(coords.x, 3)` works.