[New Feature]: chan_dahdi: Allow disabling pulse or tone dialing

[InterLinked1]

Feature Description

Currently, pulse and tone dialing are enabled on all FXS lines and there is no way to control this at all.

Adds a "dialmode" option to DAHDI that can be set to four different options:

1. both (default)
2. pulse
3. dtmf or tone
4. none

This allows for specifying, on a per-line basis, which types of signaling methods are allowed on FXS lines. Additionally, the dialmode can be updated during a call.

Imported from: https://issues.asterisk.org/jira/browse/ASTERISK-29992