feat(build_tokens): constants for build tokens + refactor login type

[ecrupper]

Types PR for Epic 1: Build Tokens.

Changes:

• library.Login type has been changed to library.Token to be more general, as there will be multiple token types.
• new token type constants, which will be declared as claims in JWT tokens created and distributed by token manager.
• user hash field being deprecated, as its previous purpose was to be a signing key for all user access tokens for a single user. Going forward, we will be using a single private key in the server env to generate all tokens.

[codecov]

Codecov Report

Merging #276 (5677451) into main (78d266f) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #276      +/-   ##
==========================================
- Coverage   96.93%   96.93%   -0.01%     
==========================================
  Files          57       57              
  Lines        6306     6303       -3     
==========================================
- Hits         6113     6110       -3     
  Misses        143      143              
  Partials       50       50              

Impacted Files	Coverage Δ
database/user.go	87.83% <ø> (-0.25%)	⬇️
library/user.go	100.00% <ø> (ø)
library/token.go	100.00% <100.00%> (ø)