Checklist

• I am sure the error is coming from Pyrogram's code and not elsewhere.
• I have searched in the issue tracker for similar bug reports, including closed ones.
• I ran pip3 install -U https://github.com/pyrogram/pyrogram/archive/develop.zip and reproduced the issue using the latest development version.

Description

When a RPC UnknownError is raised, Pyrogram tries to open and write in unkown_errors.txt in the current directory. If Pyrogram has no write access to current directory, the program crash, and the only error logged is a permission denied error, without any information on the UnkownError.

Pyrogram should not require write access to current directory and should use standard Python tools for logging. Pyrogram can configure a default logging handler for unkown rpc errors to current directory, but in any case it should use the standard python logging so users can configure another handler.

Steps to Reproduce

I don't know how to reproduce an unkown RPC error, because I cannot read the log to understand mine.

Traceback

File "virtualenv/lib/python3.7/site-packages/pyrogram/session/session.py", line 439, in send
    raise e from None
File "virtualenv/lib/python3.7/site-packages/pyrogram/session/session.py", line 436, in send
    return self._send(data, timeout=timeout)
File "virtualenv/lib/python3.7/site-packages/pyrogram/session/session.py", line 423, in _send
    RPCError.raise_it(result, type(data))
File "virtualenv/lib/python3.7/site-packages/pyrogram/errors/rpc_error.py", line 74, in raise_it
    is_unknown=True)
File "virtualenv/lib/python3.7/site-packages/pyrogram/errors/rpc_error.py", line 50, in __init__
    with open("unknown_errors.txt", "a", encoding="utf-8") as f: