Add msg support for y axis type

[Steve-Mcl]

closes #1253

Description

adds

• support for y-axis key and msg. (could not think how str would work!

fixes

• fixes x-axis msg.xxx evaluation. Previously it was using the simple getProperty and trying to get msg.payload.payload.x now it uses the RED util function to correctly evaluate the prop

• y-axis not being hidden when series is set to JSON type

• string type for x-axis not working as expected

  • e.g. on < v1.17.0, import the bar chart example and set the x-axis to string "USA" - we get a timestamp number

• line chart example

  • was configured to use msg.datestamp
  • now that evaluating msg. is fixed, this breaks the example (it was working by accident)

• scatter chart example

  • was configured to use msg.x but now that evaluating msg. is fixed, this breaks the example (it was working by accident)

• bar chart example:

  • is configured to use msg.category (should really be key: category)
  • now that evaluating msg. is fixed, this breaks the example (it was working by accident)

• Other

  • included a Clear inject on all three examples (save questions on the forum)
  • remove duplicate payload+datapoint merges when processing an array of points

Related Issue(s)

#1253

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label

[Steve-Mcl]

switching to draft until I can add "before tests" - want to ensure no breaking changes (apart from where something is fixed)