Draft: revisit interpret inner gotpl

What does this MR do and why?

Avoid json serialistaion/deserialisation in interpret-inner-gotpl, pass the result in a input value.

It bring some performance gain, but not so huge:

3 runs of time helm template . --values management.values.yaml on current main gave:

real    0m9,329s
user    0m12,109s
sys     0m0,181s

real    0m9,536s
user    0m12,383s
sys     0m0,157s

real    0m9,340s
user    0m12,133s
sys     0m0,150s

And with current branch:

real    0m8,874s
user    0m11,481s
sys     0m0,181s

real    0m9,009s
user    0m11,633s
sys     0m0,204s

real    0m8,841s
user    0m11,434s
sys     0m0,190s

/cc @tmmorin