Add repeats to entity declarations in ioc.yaml

[gilesknap]

This is to allow repeating elements in ioc.yaml.

(details to be reviewd)

Add a new field repeat of type list to entity that allows you to iterate over a list and instantiate a number of the same entity. The context for each step will include the variables val and idx which can be used to differentiate the individual entities.

examples:

  - type: ADCore.NDPvaPlugin
    repeat: {{ range(5) | list }} 
    NDARRAY_PORT: DET.CAM
    P: BL47P-EA-DET-01
    PORT: DET.PVA{{ repeate.val }}
    R: ":TX{{ repeat.val }}:"
    PVNAME: BL47P-EA-DET-01:TX{ repeat.val }}:PVA

  - type: epics.dbpf
    repeat: [ hello, world ]
    pv: BL47P-EA-DET-01:WORD{{ repeat.num }}
    value: "{{ repeat.val }}"

[gilesknap]

And combining this with #257 we could do

ioc.yaml

  - type: epics.dbpf
    repeat: {{ env.words | list }}
    pv: {{ env.prefix }}:WORD{{ repeat.num }}
    value: "{{ repeat.val }}"

env.yaml

words: [ now, is, the, time, for, all, good ]
prefix: BL47P-EA-DET-01

[coretl]

I like the concept, but rather than a reserved argument I wonder if it would be clearer to make a nested object:

  - type: ibek.repeat
    variable: index
    values: {{ range(5) | list }}
    entity:
      type: ADCore.NDPvaPlugin
      NDARRAY_PORT: DET.CAM
      P: BL47P-EA-DET-01
      PORT: DET.PVA{{ index }}
      R: ":TX{{ index }}:"
      PVNAME: BL47P-EA-DET-01:TX{{ index }}:PVA

[gilesknap]

As agreed in G13 - we will go with this.