[Config] Render all Durations as human-readable string

[roma-glushko]

Let's render all Durations like retry.min_delay, retry.max_delay, client.timeout as human-friendly strings (e.g. 5s):

[ppmdo]

Hi, nice project!

I can take a look into this. Please assign it to me.

[roma-glushko]

@ppmdo appreciate that Pablo 🙏

[daesu]

Apologies @roma-glushko @ppmdo I didn't see you had taken this. I have a PR here

[roma-glushko]

Closed in #253 ✅