testing/couchdb: new aport

The Apache CouchDB database. This is technically a draft, but it should run to my understanding. After it's merged I (and a few others) will test the package and issue an -r1 if needed.

The weirdness with fhs is because /opt/alpine is the correct place to install "self-contained" packages, such as OTP releases.

The structure of the directories below /opt/<PROVIDER> is left up to the packager of the software, though it is recommended that packages are installed in /opt/<PROVIDER>/<PACKAGE> and follow a similar structure to the guidelines for /opt/<PACKAGE>. A valid reason for diverging from this structure is for support packages which may have files installed in /opt/<PROVIDER>/lib or /opt/<PROVIDER>/bin.

Under that basis I'd be willing to move /var/lib/couchdb to /var/opt/lib/couchdb (or, ideally, /srv, which is technically the more correct location for the data files) and /etc/couchdb.d to /etc/opt/couchdb. The reasoning behind the current choices is to provide a more "native feel" to consumers of the package.