vyos-dhcp: T0: rename "DHCP Server" column to "Lease Time"

[vanitypurpose]

Change summary

Fix-up show dhcp client leases to show the lifetime with the correct key.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

Related PR(s)

How to test / Smoketest result

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[github-actions]

👍
No issues in PR Title / Commit Title

[vanitypurpose]

I have read the CLA Document and I hereby sign the CLA

[github-actions]

CI integration ❌ failed!

Details

CI logs

• CLI Smoketests (no interfaces) ❌ failed
• CLI Smoketests VPP ❌ failed
• CLI Smoketests (interfaces only) ❌ failed
• Config tests ❌ failed
• Config tests VPP ❌ failed
• RAID1 tests ❌ failed
• TPM tests ❌ failed

[sever-sever]

Re-read please contributing document https://github.com/vyos/vyos-1x/blob/current/CONTRIBUTING.md#prepare-patchcommit

and create please a task on the development portal (forge)
Refer to the correct task number instead of T0