In the Indexer Storage API, most `get` methods (eg. `content_ctags_get`) yield items with this format:
```
{"id": sha1, "tool": TOOL, "ctags": ctags1}
{"id": sha1, "tool": TOOL, "ctags": ctags2}
```
Starting with T782/D301, `content_fossology_license_get` yields item with this format:
```
{sha1: {"tool": TOOL, "licenses": [license1, license2]}}
```
---
This task is twofold:
* first, improve `content_fossology_license_get`'s result to return a dictionary instead of yielding dictionaries each with a single key-value
* secondly, refactor other `_get` methods to use the same format.
The files that should be edited are:
* `swh/indexer/tests/storage/test_storage.py`: this are the test cases for both Indexer Storage implementations. It should be adapted to test for the new format.
* `swh/indexer/storage/in_memory.py`: a fully in-memory implementation of the Indexer Storage. This is the easiest implementation to start with.
* `swh/indexer/storage/__init__.py` and ` swh/indexer/storage/converters.py`: an implementation of the Indexer Storage backed by postgresql. Look at D301 for examples of how to do it.