Where to put "constants"?

Imagine I have a value that is used all over my code, e.g. a date formatting template, a copyright notice or a company name - something like that.

Where would I put such “constants” that I use all over my code?
Do I create a provider/service for these?

In general, I would say “yes”. One thing to beware of is that const in JavaScript is less than worthless. If I absolutely, positively need something to be immutable, I expose it as a function:

foo(): string {
  return "foo";

Also, specifically speaking to one of your examples: the date formatting template, if you’re using a pipe to format dates, I would put it in that pipe instead.