feat: refactor config for more extensibility

[ZinoKader]

• config YAML is built from a Config struct
• moved config-related things to its own package

[codecov]

Codecov Report

Merging #51 (2ed0248) into develop (11a72a8) will increase coverage by 8.69%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #51      +/-   ##
===========================================
+ Coverage    31.30%   40.00%   +8.69%     
===========================================
  Files            6        6              
  Lines          230      230              
===========================================
+ Hits            72       92      +20     
+ Misses         138      111      -27     
- Partials        20       27       +7     

Impacted Files	Coverage Δ
portal/portal.go	36.11% <0.00%> (+36.11%)	⬆️
portal/config.go	100.00% <0.00%> (+100.00%)	⬆️

[mellonnen]

LGTM, but I think the config package belongs in the cmd/portal folder. And TBH the UI package should probably be in that folder as well