mumble: add portaudio build option

[tibequadorian]

jack option is already described

General

• This is a new package and it conforms to the quality requirements

Have the results of the proposed changes been tested?

• I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
• I generally don't use the affected packages but briefly tested this PR

[ericonr]

This changes package metadata, so it should be revbumped. Can you explain why you want to make it optional?

[tibequadorian]

why you want to make it optional?

I want to remove the portaudio dependency on my system and why not? JACK is optional too.