Create class for the areaDetector statistics plugin.

[jwlodek]

Several of our beamlines make extensive use of the statistics plugin to collect metadata (max pixel value, average value, etc.). We should add support for using this plugin with ophyd-async.

[callumforrester]

Reviewers: @RobertSchaffer1 @DiamondJoseph

[DiamondJoseph]

Here's my incredibly naive initial thoughts on it

#178

We want to be able to instantiate various AreaDetector implementations optionally with the Stats plugin (and likely other plugins in a chain later) and have an easy way of adding them to the scalar_signals of the detector (probably non-scalar too).

[DiamondJoseph]

@jmaruland is this still ongoing?

[ZohebShaikh]

closed by #468