Fix: DECK_KONNECT_ADDR in Konnect how tos

## Jobs to be done (optional)
If you're using a region other than `us` and decK, our how tos are missing `DECK_KONNECT_ADDR`, which prevents decK from finding the CP.

## Definition of done
- How tos that use decK and Konnect need an additional env var export in the prereq: `export DECK_KONNECT_ADDR=https://sg.api.konghq.com` (replacing the region code with their own)
- Test all the how tos after making the change

## Information
Slack: https://kongstrong.slack.com/archives/C0907DWB5T8/p1758903901879619

## Due date (optional)

ASAP

## Size
Medium (to account for testing)

Find the how-to documents that use decK with Konnect and inspect their prerequisites. Add the specified DECK_KONNECT_ADDR export using the reader's region, then test all affected how tos to confirm decK can find the control plane.

Written by the indexing model from the issue text.