DOC-1060: Update DHL credentials to medium tier template

[freakwriter]

Incorporated prerequisites in main auth method, added detailed numbered steps (what a horrible UI they have), and more definitive guidance on the API to select.

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Overall readability score: 43.11 (🟢 +0.03)

File	Readability
dhl.md	73.95 (🟢 +31.05)

View detailed metrics

🟢 - Shows an _increase_ in readability 🔴 - Shows a _decrease_ in readability File | Readability | FRE | GF | ARI | CLI | DCRS --- | --- | --- | --- | --- | --- | --- [dhl.md](https://github.com/n8n-io/n8n-docs/blob/5167123324ed03fb3302b85f94d015a8b963e967/docs/integrations/builtin/credentials/dhl.md "docs/integrations/builtin/credentials/dhl.md") | 73.95 | 53.47 | 7.03 | 9.1 | 10.29 | 6.78   | 🟢 +31.05 | 🟢 +27.1 | 🟢 +3.7 | 🟢 +6 | 🟢 +5.18 | 🟢 +1.31 Averages:   | Readability | FRE | GF | ARI | CLI | DCRS --- | --- | --- | --- | --- | --- | --- Average | 43.11 | 34.82 | 11.67 | 14.88 | 14.36 | 8.54   | 🟢 +0.03 | 🟢 +0.02 | 🟢 +0 | 🟢 +0.01 | 🟢 +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