Fix constant plandifferences in multi-line expressions

[janakerman-form3]

Relates to inuits#15

• Fixes by standardising expressions before comparing state + local TF (surpressDifFunc) using promql packages
• Adds test covering fix
• Adds failing test showing that expression format changes are not applied
  • I'm not sure that this is the right approach as changes to alert rule formatting in the source TF will result in no plan.
    • Options:
      1. Use StateFunc to normalise API response (i.e remove the blank from the rule expression in the response) when saving to state. The consequences of this will be that a user plan will always show differences if they include blank lines in their expressions. ValidateFunc could be used to enforce that no newlines are present in alerts, but this doesn't feel quite right.
      2. Simply document that modifying the alert formatting will not result in a change.
      3. Investigate why Cortex adds a newline into multi-line alerts.