test: connect to coap.golioth.dev, instead of .io

[ncmiller]

The intent is to run the end-to-end hardware tests nightly against the Golioth dev server, to catch incompatibilities/issues before the changes hit prod.

Added comments to the CI workflow files to make it clear that the device credentials should come from the dev server.

Outside of the repo, the credentials YAML file was updated on self-hosted runners.

Signed-off-by: Nick Miller nick@golioth.io

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 25400d4):

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