fix: increase default SMTP timeout

[miaulalala]

These are the RFC recommendations:

Recommended Timeout Values:
    Initial Connection: Set the timeout for the initial 220 message to at least 5 minutes.
    Mail Commands: Allocate a minimum of 5 minutes for both the MAIL and RCPT commands.
    Data Initiation: Allow at least 2 minutes for initiating the DATA command.
    Data Block: Set a timeout of at least 3 minutes for sending a data block.
    Data Termination: Provide a generous 10-minute timeout for terminating the DATA command.
    Server Timeout: Configure the server to have a timeout of at least 5 minutes.

We have to be cognizant of the PHP timeout, so 5 minutes are out.

20 seconds to start, otherwise we need to see what else we can do and if we need to recommend higher PHP timeouts as well as a higher SMTP timeout for the Mail app.

[miaulalala]

/backport to stable4.0

[ChristophWurst]

👍 does it influence autodiscovery?

[miaulalala]

👍 does it influence autodiscovery?

No, the Isp query runs via Guzzle

[ChristophWurst]

I meant https://github.com/nextcloud/mail/blob/main/lib/Service/AutoConfig/ConnectivityTester.php but the timeout is static