Fix HTTP endpoint variable resolution when value contains leading slash

[VadymKostenkoTestlum]

Problem

When using variables inside HTTP endpoint attributes, the behavior is inconsistent depending on whether the variable value contains a leading slash (/).

Current behavior

This works:

<var name="resourceEndpoint">
    <constant value="api/test/auth/jwt/resource"/>
</var>

<http alias="MEGA_APP">
    <get endpoint="/{{resourceEndpoint}}">
        <response code="200"/>
    </get>
</http>

But this more natural form does not work as expected:

<var name="resourceEndpoint">
    <constant value="/api/test/auth/jwt/resource"/>
</var>

<http alias="MEGA_APP">
    <get endpoint="{{resourceEndpoint}}">
        <response code="200"/>
    </get>
</http>

Expected: both "/{{var}}" and "{{var}}" should work the same way regardless of whether the variable value starts with "/".

Suggestion: normalize endpoint handling during variable substitution.