Add lambda functions to create ProcessGraph

[danlooo]

This PR adds support to create a ProcessGraph using lambda like syntax.
This is a generic to the functions defined for a DataCube.
We use ProcessGraph(42 * log(value,3)) instead of x -> 42 * log(x, 3), because most Julia fucntions are not supported by openEO.

using OpenEOClient
using ArchGDAL
using YAXArrays
using GLMakie

con = connect("openeo.dataspace.copernicus.eu/openeo", "", OpenEOClient.oidc_auth)
s1 = con.load_collection(
    "SENTINEL1_GRD",
    BoundingBox(west=11.293602, south=46.460163, east=11.382866, north=46.514768),
    ["2021-01-01", "2021-01-08"];
    bands = ["VV", "VH"],
    properties = Dict("sat:orbit_state" => ProcessGraph(value == :ASCENDING))
)
s2 = con.sar_backscatter(s1; coefficient="sigma0-ellipsoid", elevation_model="COPERNICUS_30")
s3 = con.apply(s2, ProcessGraph(10 * log(value, 10)))
s4 = con.save_result(s3, "GTiff")
path = con.compute_result(s3)
ds = open_dataset(path) 
plot(ds.Gray)

Example taken from python client

[danlooo]

Issue: Can't implement conditionals in Julia (e.g. overload ternary operator). Thepython client just defines a new function if_