feat: unify stac harvester and stac provider functionality

[michaelmattig]

Here is a brief summary of what I did:

[coveralls]

Coverage Report for CI Build 30352679882

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage decreased (-0.4%) to 87.064%

Details

• Coverage decreased (-0.4%) from the base build.
• Patch coverage: 979 uncovered changes across 7 files (1265 of 2244 lines covered, 56.37%).
• 38 coverage regressions across 6 files.

Uncovered Changes

File	Changed	Covered	%
geoengine/services/src/cli/stac_harvester/harvest.rs	951	237	24.92%
geoengine/services/src/cli/stac_harvester/discover.rs	615	452	73.5%
geoengine/services/src/datasets/external/stac/common.rs	592	499	84.29%
geoengine/services/src/cli/stac_harvester/mod.rs	6	0	0.0%
geoengine/operators/src/source/gdal_worker_process/process_impl.rs	7	6	85.71%
geoengine/services/src/bin/geoengine-cli.rs	1	0	0.0%
geoengine/services/src/cli/stac_import.rs	9	8	88.89%
Total (9 files)	2244	1265	56.37%

Coverage Regressions

38 previously-covered lines in 6 files lost coverage.

File	Lines Losing Coverage	Coverage
geoengine/datatypes/src/raster/masked_grid.rs	30	66.67%
geoengine/operators/src/cache/shared_cache.rs	2	85.03%
geoengine/operators/src/source/gdal_worker_process/process_impl.rs	2	92.6%
geoengine/services/src/datasets/external/stac/loading_info.rs	2	86.21%
geoengine/datatypes/src/raster/operations/grid_blit.rs	1	94.66%
geoengine/services/src/api/handlers/tasks.rs	1	99.77%

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Coverage Stats

Relevant Lines:	143318
Covered Lines:	124779
Line Coverage:	87.06%
Coverage Strength:	473415.94 hits per line

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💛 - Coveralls