Add async function for `get`

[JakobDev]

Current behavior

TranslateService has the method get which returns an Observable of the translation.
If you want to use this in a async function, you need to wrap it into firstValueFrom. e.g.

await firstValueFrom(this.translateService.get("key"));

Expected behavior

There should be an async function that does the same as get but which returns a Promise instead of an Observable. e.g.

await this.translateService.getAsync("key");

What is the motivation / use case for changing the behavior?

I use a async a lot, so I need the firstValueFrom wrapper in a lot of places. If I create a custom function (see below) I would need to use _ every time to mark the translation.

How do you think that we should implement this?

public async getAsync(key: string | string[], interpolateParams?: InterpolationParameters): Promise<Translation> {
  return firstValueFrom(this.get(key, interpolateParams));
}