Virtualize tileindex

[goergen95]

Instead of writing the tileindex for raster resources to disk (which actually requires reading them from disk for every asset) the tile-indices are now added to a portfolio as an sf object directly. This omits reading from disk, but also requires to run get_resources() for each resource that is required because the add_resource argument to init_portfolio() no longer makes sense. This argument, however, has caused more confusion (see e.g. #91 and #92) than providing benefit so it seems ok to deprecate it.

[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (755cd8b) 74.68% compared to head (1363da9) 74.71%.

Files	Patch %	Lines
R/calc_indicators.R	89.47%	2 Missing :warning:
R/get_resources.R	92.85%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #219 +/- ## ========================================== + Coverage 74.68% 74.71% +0.02% ========================================== Files 43 43 Lines 1833 1815 -18 ========================================== - Hits 1369 1356 -13 + Misses 464 459 -5 ```

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[goergen95]

Are there any objections to merging this @karpfen and @Jo-Schie?

[Jo-Schie]

I personally think this is the cleaner approach. However I just want to raise the attention that you might need to update the documentation if the tile-index is used somewhere...