[BUG] Incorrect source status upon replacement of a source in a tailer

[deadok22]

When a LogSource gets replaced in a Tailer, the new LogSource's LogStatus gets stuck in IsPending. This is presented to users in the output of agent check, which causes confusion.

The only place where LogSource is replaced is here.
The only place where the LogSource status is updated is in Tailer.Start.

Here's an example of what agent check displays in such cases (note the Status: Pending line):

  post--qa/post--post-jobalerts-cmhqa-cb666445c-fnnxq/main
  --------------------------------------------------------
    - Type: file
      Identifier: ac2e1ebc8c3f8c17a113fc57dc865d94ffb78d0f4cb06716d3356620aa6c5657
      Path: /var/log/pods/post--qa_post--post-jobalerts-cmhqa-cb666445c-fnnxq_caaa42a2-74bb-42f4-8f58-30b398a2e15f/main/*.log
      Service: postdaemon
      Source: java
      Status: Pending
        1 files tailed out of 1 files matching  
      Bytes Read: 297770   
      Pipeline Latency:
        Average Latency (ms): 0
        24h Average Latency (ms): 0
        Peak Latency (ms): 0
        24h Peak Latency (ms): 0