Implement static lease

[benbjohnson]

This adds support for a fixed primary node so that Consul does not need to be used. It will not support handoff of the primary so the cluster will be read-only when the primary stops.

Original PR: jwhear#2

Fixes #37

Usage

Specify the static block in your configuration instead of consul. You cannot specify both blocks.

Primary node

static:
  primary: true
  primary-url: "http://myhost:20202"

Replica nodes

static:
  primary: false
  primary-url: "http://myhost:20202"

[benbjohnson]

@jwhear I reworked your Fixed Leader PR a bit. I changed the name to "static" instead of "fixed", I removed the UUID & HTTP call in the leaser, and I added a test to verify.

[benbjohnson]

@jwhear Hmm, it like it's still not showing attribution. Do you have your email hidden or are you using a different email address than the gmail.com one that's on your commit? It doesn't look like it's linking your name to your GitHub account either on the UI.

[jwhear]

Looks like I had a different email on file with Github; I've added the one used in my commits.

[jwhear]

Also, regarding the UUID business: I went back and forth on whether to use a config value or do self-discovery and ended up with the self-discovery because it meant that my config file could be the same for all nodes. Not a big deal either way though. Might be good to allow setting primary: true via an environment variable as well.

[benbjohnson]

That makes sense. LiteFS will evaluate environment variables in the config so you can do: primary: ${IS_PRIMARY}