contract/contract_forecast/views/contract.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2019 ACSONE SA/NV
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<odoo>

    <record model="ir.ui.view" id="contract_contract_form_view">
        <field name="name">contract.contract.form (in contract_forcast)</field>
        <field name="model">contract.contract</field>
        <field name="inherit_id"
               ref="contract.contract_contract_form_view"/>
        <field name="arch" type="xml">
            <xpath expr="//div[@name='button_box']" position="inside">
                <button class="oe_stat_button" type="object"
                        icon="fa-area-chart"
                        name="action_show_contract_forecast"
                        help="Forecast">
                    <div class="o_form_field o_stat_info">
                        <span class="o_stat_text">Forecast
                        </span>
                    </div>
                </button>
            </xpath>
        </field>
    </record>


</odoo>