add ptycho-style snake grid plan

[prjemian]

This is an upgrade on the linear moves of the trajectory plan. Logically, it follows #43 where the list of waypoints (time, position) is loaded into the IOC.

https://github.com/BCDA-APS/bdp_controls/blob/4d03dc272e584dabe8d5b079f4335cbe59d7ea31/qserver/instrument/plans/trajectories.py#L15-L18

[prjemian]

See example: https://github.com/BCDA-APS/bdp_controls/issues/41#issuecomment-1151666671

Checked with our Ptycho team. This is similar to what they use now but this is a rectangle, they use a spiral with a width.

[prjemian]

Here's an example set of 249 such (x,y) points, connected by lines:

[prjemian]

For M5, we'll move through the waypoints from a custom bluesky plan. In M6, we'll move that into the IOC.