Ending separate distribution of raft

[cole-miller]

The dqlite team has decided to end separate maintenance and distribution of our Raft library. We have imported the libraft sources into the dqlite repository, and as of version 1.16.4 the dqlite build system includes an --enable-build-raft option to compile these sources as part of libdqlite instead of finding libraft with pkg-config; this is now the preferred way to build dqlite.

The canonical/raft repository will no longer be updated or accept contributions, but will remain readable and available to fork on GitHub. A maintained fork from @freeekanayaka can be found at cowsql/raft, and we recommend that you switch to this fork if you previously depended on canonical/raft directly.

If you have any questions about these changes, or if you've encountered a problem when migrating to --enable-build-raft, please post here and we'll be happy to help.

[cole-miller]

Note that for now we still support linking to a separately-compiled libraft when building dqlite. This remains the default for the configure script (if you don't pass --enable-build-raft) and we test it in CI.

In the future, the option to link against an external libraft will go away, and --enable-build-raft will be the default.