[Task]: Update ADR template and process

[widal001]

Summary

Update the ADR template to reflect the new baseline acceptance criteria. Also document the proposed process in documentation/decisions/README.md

Acceptance criteria

• When a new ADR ticket is created it defaults to the following acceptance criteria:
  • The approvers for this decision have been identified (ideally before work on the ADR starts)
  • The ADR is created and stored in documentation/decisions/adr with status "Accepted"
  • The ADR has been reviewed and approved by the approvers listed above
  • The ADR satisfies requirements that are outlined in the ADR template
  • Any follow-up tickets have been created (if necessary)
• The ADR ticket also has a space to identify the approvers of this decision
• The process for creating, reviewing, and approving an ADR is outlined in documentation/decisions/README.md
• All stages before Accepted have been removed from the ADR template