Store & read in-memory cache on local disk

When a Function stops running, the in-memory cache will also be cleared.

For us to have the least amount of hits to Cosmos DB, the cache can be stored & read from the local disk.
As proofed in this repository: https://github.com/Jandev/poc-scale-infinite-shared-state the state should be stored in:

> Sharing date has to be done in the `D:\home\data\`-folder.

The state can be stored as a human-readable JSON document, called `cache.json`.
The contents will look like

```json
{
"entries": [
{
"slug": "the-slug",
"fullUrl": "https://the-full-url/"
}
]
}
```
Additional properties can be added when necessary, like an `updatedOn`.

Start by locating the Azure Function's in-memory cache and Cosmos DB access paths, then inspect how cache state is initialized and cleared. Persist and reload the entries in D:\home\data\cache.json using the shown schema, and verify that the cache survives a Function restart while retaining the expected URL mappings.

Written by the indexing model from the issue text.