snapcast: update to 0.28.0

[amak79]

Testing the changes

• I tested the changes in this PR: briefly

This release no longer bundles the pre-built Snapweb. When accessing the Snapweb page, you are now greeted with the following notice.

This is a placeholder for Snapweb, a web based control client and player for Snapcast.
To install Snapweb, please follow these steps:

    1. Download Snapweb on the Snapweb release page. You can either download
        * snapweb.zip and extract it on your Snapcast server machine, e.g. into /usr/share/snapserver/snapweb or
        * snapweb_x.y.z-1_all.deb and install it with sudo apt install ./snapweb_x.y.z-1_all.deb to /usr/share/snapweb
    2. Configure the document root (doc_root, see below) in the snapserver configuration file snapserver.conf — usually located in /etc/snapserver.conf — to the location where snapweb is extracted or installed.
    3. Restart Snapserver to activate the changes: sudo service snapserver restart

What should we do with Snapweb?

1. Leave the snapcast package as is and let the user fetch and extract the pre-built Snapweb as per instructions.
2. Fetch and install the pre-built Snapweb from the snapserver subpackage.
3. Create a new snapweb package and build it from source. The user can then install it if needed.

[the-maldridge]

This feels similar conceptually to grafana's assets package, where we use the pre-built one due to the complexity of getting large javascript projects to build reliably. I would advise you to create a new package that just pulls in their pre-built package and puts it in the right place.

[amak79]

If we go the separate package route, there will be a file conflict as both packages install index.html in /usr/share/snapserver/snapweb. Perhaps it's better to go with option 2?

[amak79]

I've implemented option 2 because of the file conflict. The resulting package is now equivalent to Snapcast <=0.27.0 where pre-built Snapweb is bundled.