feat: simplify using Test DC

[KnorpelSenf]

Requested in https://t.me/grammyjs/190672

Use it like so:

const bot = new Bot("token", {
    client: { environment: "test" },
});

[Loskir]

Maybe rename dc to environment? Data center is a different entity
This update is also not backwards compatible for those who use buildUrl

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (4f730f1) 46.33% compared to head (ac9f31c) 46.33%.

Files	Patch %	Lines
src/core/client.ts	50.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #509      +/-   ##
==========================================
- Coverage   46.33%   46.33%   -0.01%     
==========================================
  Files          19       19              
  Lines        5659     5672      +13     
  Branches      227      228       +1     
==========================================
+ Hits         2622     2628       +6     
- Misses       3034     3041       +7     
  Partials        3        3              

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[KnorpelSenf]

Maybe rename dc to environment?

Hmm yes that's a better name, let me rename it.

This update is also not backwards compatible for those who use buildUrl

That is not correct, you can always omit the parameter when specifying a function. () => "" is assignable to (a: number, b: number, c: number) => string.