Review tags for elevation to the core spec

[j616]

Context
Tags are often used in TAMS to explore features before committing to baking them into the spec. Some tags in this class have been in use for some time now (e.g. flow_status). We should review our tags listing and elevate tags to the core spec where appropriate.

Actions

• Review tags for potential elevation to the core spec
• Write and ADR documenting the decision process for candidates for elevation
• Review this with the TSC, and wider community as appropriate
• Make the relevant spec changes, and changes to AppNote0003

Outcome
Tags have been reviewed for elevation to the core spec, and elevated as appropriate.

[johnbilt]

The flow_status is a good candidate for elevation as there are now multiple solutions using this to detect whether a flow is currently ingesting or closed. There are a few interesting extensions on this one that probably should be discussed including whether the store should actively do anything with this tag (eg close it after a period of time) or leave for the ingest tool to deal with. Also there has been request to roll the status up from the flows to an overall status at the top source level. So needs scoping and discussion and may be worth creating it's own ticket

[j616]

Another consideration on flow_status is where an ingester is being swapped out without interruption of the ingest. The clean shutdown of the initial ingester might currently result in a closed_complete. One option would be to drop the status back to awaiting_content. Or we could consider adding a further state to aid in that handover.