Interrogate step labels

[yjunechoe]

A small surgery on interrogate() to:

1. Toggle the printing of each step's label to the console output during interrogation (Show labels in console output when using interrogate() #510)
2. Expose the internal quiet variable to let users control whether interrogate() should print to console at all (now becomes interrogate(progress = interactive()))

Also works good with glue integration from #495 !

create_agent(small_table) %>% 
  col_exists(
    columns = c(a, z),
    label = "Check that column `{.col}` exists",
    actions = action_levels(notify_at = 1)
  ) %>% 
  col_exists(
    columns = x,
    label = "`x` should really exist",
    actions = action_levels(stop_at = 1)) %>% 
  col_vals_not_null(
    columns = c:e,
    label = "Checking that {.col} is complete",
    actions = action_levels(warn_at = 1)
  ) %>% 
  interrogate(show_step_label = TRUE)
#> 
#> ── Interrogation Started - there are 6 steps ────────────────────────────────────────────────────────
#> ✔ Step 1: OK. — Check that column `a` exists
#> ! Step 2: NOTIFY condition met. — Check that column `z` exists
#> ✖ Step 3: STOP condition met. — `x` should really exist
#> ! Step 4: WARNING condition met. — Checking that c is complete
#> ✔ Step 5: OK. — Checking that d is complete
#> ✔ Step 6: OK. — Checking that e is complete
#> 
#> ── Interrogation Completed ──────────────────────────────────────────────────────────────────────────

Fixes: #510

[rich-iannone]

LGTM!