feat!: add default connect and read timeout

[paalbra]

I've experienced that the Zabbix API sometimes hang. I believe this is due to some database related issues (hang on write operations only).

If someone encounter this problem a script using pyzabbix might hang forever if you forget to add a timeout parameter:

pyzabbix/pyzabbix/api.py

Lines 61 to 64 in 962693d

	:param timeout: optional connect and read timeout in seconds, default: None
	If you're using Requests >= 2.4 you can set it as
	tuple: "(connect, read)" which is used to set individual
	connect and read timeouts.

The requests quickstart says the following about the timeout parameter:

Nearly all production code should use this parameter in nearly all requests. Failure to do so can cause your program to hang indefinitely

Following this guide I think that pyzabbix should have some kind of default, rather than None.

Also quoting from the quickstart:

timeout is not a time limit on the entire response download; rather, an exception is raised if the server has not issued a response for timeout seconds (more precisely, if no bytes have been received on the underlying socket for timeout seconds). If no timeout is specified explicitly, requests do not time out.

I think that a timeout of 30 seconds will be a very, very conservative default, but it should prevent that someone that forget to set a timeout encounter scripts that hang for ever.

[jooola]

This would be a breaking change and should be part of a v2.