adapt s2 importer to work without Google BigQuery

[griembauer]

This PR adapts the actinia importer process for the importing of Sentinel-2 data. Sentinel-2 data (indicated by a scene-ID) can now be imported directly from Google Cloud Storage without providing any credentials using i.sentinel.download and i.sentinel.import in the background. This PR currently uses the standard implementation of the importer: each import_description can be used to import exactly ONE raster map. For Sentinel-2 data, this means that each band has to be specified individually.

Note: The current implementation (query via Google Cloud BigQuery interface etc.) is not removed in this PR, the new functionality without login is simply added.

perspective TODOs:

• implement extent (bbox): import processes are automatically put before grass (or other) processes in a process chain. This means that no region can be set via a grass module before running the import. Limiting the import data to a certain extent has to be done via the extent parameter of the importer. This still needs to be implemented.
• correct null value: When importing a scene, i.sentinel.import reprojects the map if it does not match the current projection. This may interfere with 0-values, that should be treated as NULL-values and removed via r.null or i.zero2null. This problem should probably be solved in r.import
• improve i.sentinel.download such that it can directly download individual bands (and required metadata) instead of the entire scene, (and maybe even cut it to the current region)
• implement query such that all S2 data from region and time of interest are imported (e.g. using i.sentinel.coverage + t.sentinel.import). This is currently implemented with the BigQuery approach and should be replaced.

Example PC:

{
 "list": [
          {"id": "importer_1",
          "module": "importer",
          "inputs": [{"import_descr": {"source": "S2B_MSIL1C_20210809T101559_N0301_R065_T32UNB_20210809T124430",
                                       "type": "sentinel2",
                                       "sentinel_band": "B04"},
                      "param": "map",
                      "value": "B04"},
                     {"import_descr": {"source": "S2B_MSIL1C_20210809T101559_N0301_R065_T32UNB_20210809T124430",
                                       "type": "sentinel2",
                                       "sentinel_band": "B08"},
                      "param": "map",
                      "value": "B08"}]},
          {
      			"id": "dummy_region",
      			"comment": "Set the region to raster",
      			"module": "g.region",
      			"inputs": [
      				{
      					"param": "raster",
      					"value": "B04"
      				}
      			],
      			"flags": "p"
      		},
          {
      			"id": "dummy_mapcalc",
      			"comment": "just a dummy module",
      			"module": "r.mapcalc",
      			"inputs": [
      				{
      					"param": "expression",
      					"value": "test_raster = B04 + B08"
      				}
      			]
      		}
         ],
 "version": "1"
}

[anikaweinmann]

Thank you.