Adding support for execution on slurm grids

- Adding support for SlurmTaskExecutor in `daggyd` if DAGGY_ENABLE_SLURM is defined.
- Renaming some test cases
- Enabling compile-time slurm support
- Adding slurm documentation

tests/unit_server.cpp

@@ -50,7 +50,7 @@ REQUEST(std::string url, std::string payload = "") {
     return response;
 }
 
-TEST_CASE("Server Basic Endpoints", "[server_basic]") {
+TEST_CASE("rest_endpoint", "[server_basic]") {
     std::stringstream ss;
     daggy::executors::task::ForkingTaskExecutor executor(10);
     daggy::loggers::dag_run::OStreamLogger logger(ss);