Use the user directory as default config file location

The current default(first) location for configuration storage is `./cli.json`, which is not so useful in most cases since the user would need to:
- Call gotify-cli in this specific directory for every invocation
- Create a `cli.json` in a random directory, which is not a clearly explanatory file name.

So I think in most cases, the user would use user directory as their config storage, so we should put that in front of `./cli.json` by default during initialization.

Locate the initialization and configuration path handling in the CLI, then inspect how the default locations are ordered. Verify that the user directory is checked before ./cli.json and confirm the resulting precedence during normal invocation.

Scritto dal modello di indicizzazione a partire dal testo della issue.