Document for How to setup UTF-8 supporting mode on Cortex

[SungJin1212]

Write a docs for how to configure UTF-8 support on Cortex and how this setting affects each components (Distributor, Ruler, and Alertmanager)

[RaphSku]

I'd like to work on this issue.

[SungJin1212]

@RaphSku
I assigned it to you, thanks!

[RaphSku]

@SungJin1212 Hi, just wanted to let you know that I have linked the PR, thank you.