How to limit DB resources for different applications on the same PostgreSQL server/cluster?

Question

PostgreSQL

Hello!
There are several backends that do not create a constant load on the DBMS, so it is expensive to allocate a separate server for each application.
It is convenient and inexpensive to collect all the databases in one postgres cluster, but in this case one database can put others, taking up all the CPU and memory resources.
According to the database storage, you can quote with tablespaces, but what about the CPU and memory?