Overhaul Configuration and Settings for Torrust

[da2ce7]

Our current configuration system is a mess and not sustainable.

I suggest that we move to the Figment configuration library and conceptually rework our entire approach to configuration for the tracker.

[josecelano]

Related to: #127

Subtasks (UPDATED 2024-05)

• Config overhaul: migrate to figment #850
• Config overhaul: replace primitive types in configuration with richer types #852
• Config overhaul: remove default values from config file templates #856
• Config overhaul: missing toml file location in Figment errors #855
• Config overhaul: change env var names convention #851
• Config overhaul: version 2 for the configuration toml file (breaking changes) #878

More subtasks (UPDATED 2024-07)

After an internal discussion, we decided to make more changes:

• Config overhaul: split tracker mode #932
• Config overhaul: define current config version as version 2 #939
• Config overhaul: improve admin experience #935
• Config overhaul: rename log_level to threshold #936
• Config overhaul: add version and namespace to the configuration #937
• Config overhaul: remove secrets when final config is printed to console #948
• Config overhaul: lowercase for DatabaseDriver #950
• Config overhaul: use an explicit section for metadata #958
• Config overhaul: make some fields mandatory #938