feat: add types and improved docs for API_CONSTANTS

[KnorpelSenf]

Exports DEFAULT_UPDATE_TYPES from grammY.

Exports a new interface ApiConstants which provides types for API_CONSTANTS.

Closes #453 which has several problems:

• it provides two very similar interfaces called ApiConstants and API_CONSTANTS which is maximally confusing
• one of the two interfaces is not documented at all, but it is the more useful one
• there is no link from the values to the types in the generated Deno module docs

This PQ fixes all of that.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.11% 🎉

Comparison is base (5a0064d) 46.40% compared to head (9abf868) 46.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #485      +/-   ##
==========================================
+ Coverage   46.40%   46.51%   +0.11%     
==========================================
  Files          19       19              
  Lines        5620     5615       -5     
  Branches      224      226       +2     
==========================================
+ Hits         2608     2612       +4     
+ Misses       3009     3000       -9     
  Partials        3        3              

Files Changed	Coverage Δ
src/context.ts	24.55% <100.00%> (+0.63%)	⬆️
src/convenience/constants.ts	100.00% <100.00%> (ø)

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