Alerting: Add MissingSeriesEvalsToResolve to the APIs (#102150)

What is this feature?

A follow-up for #101184, adds AlertRule.MissingSeriesEvalsToResolve to the APIs.

missing_series_evals_to_resolve must be specified too and it must be > 0.

POST /api/ruler/grafana/api/v1/rules/{folderUID} works in the following way:

    If missing_series_evals_to_resolve is not sent or null, the rule keeps its existing value
    If missing_series_evals_to_resolve > 0: updates to that value
    If missing_series_evals_to_resolve = 0: resets to default (nil).
    AlertRule.MissingSeriesEvalsToResolve can't be 0, so I used it to reset

In the Provisioning API, the value is just set if present and > 0. Otherwise it's reset:

PUT to /api/v1/provisioning/alert-rules/{UID}:

    If missing_series_evals_to_resolve is nil, it's reset to the default value
    If missing_series_evals_to_resolve > 0, it's updated

pkg/tests/api/alerting/test-data/rulegroup-1-get.json

@@ -46,7 +46,8 @@
             "simplified_query_and_expressions_section": false,
             "simplified_notifications_section": false
           }
-        }
+        },
+        "missing_series_evals_to_resolve": 1
       }
     },
     {
@@ -93,7 +94,8 @@
             "simplified_query_and_expressions_section": false,
             "simplified_notifications_section": false
           }
-        }
+        },
+        "missing_series_evals_to_resolve": 2
       }
     }
   ]