Add simple way to add a common data source

We have 100 existing reports in another tool.
We want to replace them with PowerBI reports.
We want to have a common data source for the PowerBI reports and not have to reenter and costly maintain the credentials for each report.
We want the credentials to be common read only report user and not expire with the Active Directory credentials of the report author.
We use Microsoft SQL Server and create reports using two different read only databases.
We want *important* to not have to change each report if the SQL Server data is moved to a new SQL Server with a different SQL Server name.
We use on premise SQL Servers.

Is it possible to give a decent solution not requiring us to maintain and fix credentails for 100 reports every year or two?

Our data is in several hundred different database tables and we do not want to create a different query for each table.

PowerBI reports should be reusable, portable from user to user and something which our tech team can keep in version control.