Fix undefined client_is_lead errors

[wrongecho]

• Defines client_is_lead within the general client include file to prevent the following error filling up logs on almost every page load.

  "PHP Notice: Undefined variable: client_is_lead in itflow/client_edit_modal.php on line 111"

[sonarcloud[bot]]

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0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
3.4% Duplication

[wrongecho]

Test these changes at: https://clientisleadfix798.pr-review.itflow.org
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