Describe the bug
Each call to get_default_cli().invoke(...) will leak a file handle due to logging.

To Reproduce
Run this script under Linux:

from azure.cli.core import get_default_cli
import os
import tempfile

for _ in range(10):
    with tempfile.TemporaryFile('w+t') as temp:
        get_default_cli().invoke(["account", "show"], out_file=temp)

open_fds = os.listdir(f"/proc/{os.getpid()}/fd")
print("Leaked file handles:")
for fd in open_fds:
    try:
        target = os.readlink(f"/proc/{os.getpid()}/fd/{fd}")
        print(f"  {fd} - {target}")
    except:
        pass

Expected behavior
When the invoke() command returns, all internal resources specific to the child process are released.

Environment summary
Untunu 18.04
Python 3.6.9
azure-cli 2.3.1
azure-cli-core 2.3.1

Additional context
The problem is due to azlogging.py not cleaning up the logging.FileHandler resource allocation on line 101

I did try updating end_cmd_metadata_logging to clean up the file handler, but this method is not called if the az process errors, e.g. a problem with the user's credentials. This is because exception handling bypasses most clean up code.