`load_stac` scale and offset clarifications

[clausmichele]

1. I moved the json spec out of the proposals folder, since now the process is available on many different back-ends CDSE, VITO, openEO Platform, EODC, Eurac Research.
2. I tried to clarify the behavior of the process in case of Items/Assets with associated scale and offset parameters, which from this discussion we aggreed shouldn't be applied by default: https://github.com/Open-EO/openeo-processes/issues/503

[clausmichele]

@m-mohr what should I add to make the load_stac tests passing? I'm not sure to understand. This is also the result of a local tests run:

npm test

> @openeo/processes@2.0.0 test /home/mclaus@eurac.edu/openeo-processes/tests
> openeo-processes-lint testConfig.json

/home/mclaus@eurac.edu/openeo-processes/tests/node_modules/@jest/core/build/SearchSource.js:137
  _context;
          ^

SyntaxError: Unexpected token ;
    at Module._compile (internal/modules/cjs/loader.js:723:23)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Module.require (internal/modules/cjs/loader.js:692:17)
    at require (internal/modules/cjs/helpers.js:25:18)
    at Object.<anonymous> (/home/mclaus@eurac.edu/openeo-processes/tests/node_modules/@jest/core/build/index.js:30:44)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
npm ERR! Test failed.  See above for more details.