lineup2(): report peak statistics as additional run stream

[prjemian]

When the lineup2() plan is run, peak statistics are assessed when the stop document is received. Since lineup2() uses a standard plan (bp.rel_scan()), it cannot add additional streams to the run.

Refactor the plan so that the stats are pushed to a new stream in the still-open run.

[prjemian]

From #1044 (comment):

... reported as additional stream ...

Must replace rel_scan() plan with custom plan. The heart of bp.scan_nd() provides the basis:

    @bpp.stage_decorator(list(detectors) + motors)
    @bpp.run_decorator(md=_md)
    def inner_scan_nd():
        if predeclare:
            yield from bps.declare_stream(*motors, *detectors, name="primary")
        for step in list(cycler):
            yield from per_step(detectors, step, pos_cache)
        # TODO: write analysis to `"peak_analysis"` stream

    return (yield from inner_scan_nd())

Would need to redesign when signal_stats.analysis = is called.