Telegram expires certain links in messages after some (unknown) amount
of time; this commit is the first step to working around that by
providing an image URL proxy.
In order to do that, we tick two important boxes here:
1. Store an extensible data structure in the cache.
2. Expire them periodically.
Change-Id: Iba192d8b71db4493c942d1baf5680bd086f8f60b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5607
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
89f25b431d
