better default display name

[dirkraft]

Often in practice the metric name is the same across many series added to the same board. Often dimensions are the only part of the metric identifier that differs.

Concatenate all identifiers of a metric and then default the displayed name to portion of that string which is unique (differentiable) from all other such series identifiers (new behavior).

If that produces no string, fallback to the plain name field (existing behavior).