the following directory seems to be missing
/usr/lib/python3/dist-packages/pgactivity
you should be able to find it from the shell, inside is the file Data.py which contains the reference line mentioned in this path /usr/local/bin/pg_activity line 7 import pgactivity.Data

to correct this, just confirm that the ubuntu version of your branch is 20.04 

You cannot run the PG_ACTIVITY utility because it is not installed.

Due to our service level agreement (SLA) we do not allow additional python libraries to be installed via command line in order to maintain 99.9% Uptime.

• some well known libraries that have been audited by Odoo can be installed via a requirements.txt file in your repository, but this feature is designed for libraries that support code you are writing in modules.
  
  See https://www.odoo.com/documentation/15.0/administration/odoo_sh/advanced/containers.html for more information about the requirement.txt file

If you are interested in performance monitoring tools, please use the MONITOR tab of your branch, where you can see System metrics: 

The MONITOR tab also creates flamegraphs for you to profile your code.