DOC-1052: Update MQTT credentials to medium tier template

[freakwriter]

Convert to detailed numbered instructions. These are still fairly generic since there are a ton of providers they could be using.

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Overall readability score: 43.01 (🟢 +0)

File	Readability
mqtt.md	70.44 (🔴 -1.11)

View detailed metrics

🟢 - Shows an _increase_ in readability 🔴 - Shows a _decrease_ in readability File | Readability | FRE | GF | ARI | CLI | DCRS --- | --- | --- | --- | --- | --- | --- [mqtt.md](https://github.com/n8n-io/n8n-docs/blob/f957406d79925c9ac9d442d29b11583ce0434e74/docs/integrations/builtin/credentials/mqtt.md "docs/integrations/builtin/credentials/mqtt.md") | 70.44 | 53.68 | 7.92 | 9 | 11.16 | 7.07   | 🔴 -1.11 | 🔴 -1.01 | 🔴 -0.12 | 🔴 -0.7 | 🔴 -0.58 | 🟢 +0.34 Averages:   | Readability | FRE | GF | ARI | CLI | DCRS --- | --- | --- | --- | --- | --- | --- Average | 43.01 | 34.75 | 11.68 | 14.9 | 14.37 | 8.55   | 🟢 +0 | 🟢 +0 | 🟢 +0 | 🟢 +0 | 🟢 +0 | 🟢 +0

View metric targets

Metric | Range | Ideal score --- | --- | --- Flesch Reading Ease | 100 (very easy read) to 0 (extremely difficult read) | 60 Gunning Fog | 6 (very easy read) to 17 (extremely difficult read) | 8 or less Auto. Read. Index | 6 (very easy read) to 14 (extremely difficult read) | 8 or less Coleman Liau Index | 6 (very easy read) to 17 (extremely difficult read) | 8 or less Dale-Chall Readability | 4.9 (very easy read) to 9.9 (extremely difficult read) | 6.9 or less