In our environment we are not the tenant owners and we don't even have sharepoint admin permissions. But we are farm admins of the on-prem SharePoint 2019 environment. What kind of permissions from tenants are required to setup on-premises data gateway to consume power app platform like flow and powerapps . Where do the gateway need to be installed ? I have googled and I didn't find much information.
The Data Management Gateway should be installed on it's own server (or >1 as it supports HA). You would need Power BI Administrator rights to deploy it. From there, you can add one or more individuals to administer the gateway in the Power BI portal. These admins would have the ability to manage the Gateway in Power BI, including removing the Gateway, add/edit/delete Gateway connections, and add other administrators.
The Gateway does require Flow P1 licensing to use with Flow (same with PowerApps, but there is no direct PowerApps integration with on-prem, you'd have to initiate the usage of the PowerApps from the PowerApps portal).