Description of problem:
Connections from Pulpcore have a user agent header in their requests created from the Pulp version, the Python version, and aiohttp version. Certain network components have the ability to restrict requests by user agent fields. This request is to allow a user to set a custom user agent header value for Pulpcore to use.

Version-Release number of selected component (if applicable):

python39-pulpcore-3.21.6-1.el8pc.noarch

satellite-6.13.1-1.el8sat.noarch

How reproducible:
N/A

Steps to Reproduce:
N/A

Actual results:
User agent field is defined in this file 
/usr/lib/python3.6/site-packages/pulpcore/download/factory.py, By the following function:

def user_agent():
        """
        Produce a User-Agent string to identify Pulp and relevant system info.
        """
        pulp_version = get_distribution("pulpcore").version
        python = "{} {}.{}.{}-{}{}".format(sys.implementation.name, *sys.version_info)
        uname = platform.uname()
        system = f"{uname.system} {uname.machine}"
        return f"pulpcore/{pulp_version} ({python}, {system}) (aiohttp {aiohttp_version})"

Expected results:
A settings value on Satellite to allow user to input a custom user agent string.

Additional info:
As a workaround to allow this to work replace the following line:
        return f"pulpcore/{pulp_version} ({python}, {system}) (aiohttp {aiohttp_version})"
with:
        return f"curl/7.61.1"