feat: add log.job.dir (#1165)

`log.job.dir` makes the runner write a copy of every task's log to that directory, as `<start time>-task-<id>.log`: the rows exactly as Gitea received them, with the same masking and the job's result on the last line. Off by default, and what Gitea shows does not change.

`log.job.retention` (default `168h`) and `log.job.max_size` (default `1GB`) bound the directory. Documented in the README.

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1165
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>

internal/pkg/report/reporter_test.go

@@ -1041,18 +1041,13 @@ func TestReporter_StopHeartbeats(t *testing.T) {
 		"Close() must still send a final UpdateTask after StopHeartbeats")
 }
 
-func TestAppendIfNotNil(t *testing.T) {
-	var s []*int
-	s = appendIfNotNil(s, nil)
-	assert.Empty(t, s)
-
-	v := 7
-	s = appendIfNotNil(s, &v)
-	require.Len(t, s, 1)
-	assert.Equal(t, &v, s[0])
-
-	s = appendIfNotNil(s, nil)
-	require.Len(t, s, 1)
+func TestAppendLogRow(t *testing.T) {
+	r := &Reporter{}
+	row := &runnerv1.LogRow{Time: timestamppb.Now(), Content: "hello"}
+	r.appendLogRow(nil)
+	r.appendLogRow(row)
+	r.appendLogRow(nil)
+	assert.Equal(t, []*runnerv1.LogRow{row}, r.logRows)
 }
 
 func TestReporter_Levels(t *testing.T) {