Sources
Source procs appear at the beginning of a flowgraph to feed data points into it.
(source; source) | processor | (processor; processor) | processor | (sink; sink)
Use emit source to synthetically generate points that contain only a timestamp, to compose test/example Juttle programs.
Read data via adapters such as the built-in read file, read stochastic, read http, or plug in external adapters to read from remote backends.