HLS: Support delay cleanup for TS files.

[winlinvip]

Some player start to play from the first ts file, which might be cleanup.

It's better to delay cleanup the ts files.

[mapengfei53]

Currently, the delay deletion feature is expected to be modified into either Method 1: delay_cleanup on; or Method 2: delay_cleanup 60; (unit: s). In the first method, users can only configure to turn it on or off, with a fixed internal duration. In the second method, users can customize the delay deletion duration.