Explore: Fix label filtering for rate queries

- exclude `]` from match expression for selector injection to ignore
  range vectors like `[10m]`

public/app/plugins/datasource/prometheus/datasource.ts

@@ -39,7 +39,7 @@ export function addLabelToQuery(query: string, key: string, value: string): stri
 
   // Add empty selector to bare metric name
   let previousWord;
-  query = query.replace(/(\w+)\b(?![\({=",])/g, (match, word, offset) => {
+  query = query.replace(/(\w+)\b(?![\(\]{=",])/g, (match, word, offset) => {
     // Check if inside a selector
     const nextSelectorStart = query.slice(offset).indexOf('{');
     const nextSelectorEnd = query.slice(offset).indexOf('}');

public/app/plugins/datasource/prometheus/specs/datasource.jest.ts

@@ -351,6 +351,7 @@ describe('PrometheusDatasource', () => {
     expect(addLabelToQuery('foo{instance="my-host.com:9100"}', 'bar', 'baz')).toBe(
       'foo{bar="baz",instance="my-host.com:9100"}'
     );
+    expect(addLabelToQuery('rate(metric[1m])', 'foo', 'bar')).toBe('rate(metric{foo="bar"}[1m])');
   });
 });