Consider renaming "Instances" to "Flows"

### Description

This is going to generate a lot of heat/discussion, but it comes from a good place...

In a call today with @MichaelBDavis and some prospects, there was regular confusion over "Instance" as a term, because it was used both in discussion of the number of FlowFuse Instances they wanted to spin up as well as the number of "Node-RED Instances" they wanted running in each.

We recently had feedback in @knolleary's webinar that the switch to Hosted/Remote terminology was a good one, and from the sales conversations I've seen that is also consistent feedback there too.

Michael and I discussed the option for "Flows" and it does fit nicely - "Hosted Flows" and "Remote Flows". It also helps bridge the gap for those less familiar with Node-RED, all they care about really is the flow-based interface.

Considering the views available for a given Instance, we have:

All of these options make viable sense under the guise of a "Hosted Flow". Flows can still have multiple tabs (in the context of the NR Editor).

The main confusion could be around the term `flow.json`, but that is very niché/specific to those with Node-RED experience

Anyway, opening for consideration/discussion

### Which customers would this be available to

None

No files, tests, or entry points are named. Start by reviewing the terminology discussion and the affected Instance views described in the issue, then establish the scope and obtain agreement on the proposed naming. Done would require a decided term and an identified set of product surfaces to update.

Written by the indexing model from the issue text.