DOC-1004: Update FTP credential to medium tier template

[freakwriter]

Summary of changes:

• Added examples of FTP servers.
• Removed bullet point list entirely and converted to numbered list.
• Added guidance about when to use each type into the "Using xxx" sections.
• Added an example of how to generate private key in OpenSSH format.

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Overall readability score: 42.57 (🔴 -0.01)

File	Readability
ftp.md	65.07 (🔴 -7.25)

View detailed metrics

🟢 - Shows an _increase_ in readability 🔴 - Shows a _decrease_ in readability File | Readability | FRE | GF | ARI | CLI | DCRS --- | --- | --- | --- | --- | --- | --- [ftp.md](https://github.com/n8n-io/n8n-docs/blob/3f866e97046c3a632a5df5624d5c5c1443d86ac7/docs/integrations/builtin/credentials/ftp.md "docs/integrations/builtin/credentials/ftp.md") | 65.07 | 51.24 | 7.81 | 11.5 | 13.2 | 6.65   | 🔴 -7.25 | 🔴 -8.77 | 🔴 -0.28 | 🔴 -1.9 | 🔴 -1.79 | 🔴 -0.01 Averages:   | Readability | FRE | GF | ARI | CLI | DCRS --- | --- | --- | --- | --- | --- | --- Average | 42.57 | 34.42 | 11.74 | 14.97 | 14.43 | 8.58   | 🔴 -0.01 | 🔴 -0.01 | 🟢 +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