[exporter/splunkhec] Remove deprecated batcher config

[dmitryax]

Remove batcher field from the configuration interface which has been deprecated for a while. Users should use sending_queue::batch instead.

Migrating from batcher to sending_queue::batch

The batcher field in exporter/splunk_hec has been removed. Replace it with sending_queue::batch.

Before

  exporters:
    splunk_hec:
      token: "..."
      endpoint: "https://splunk:8088"
      batcher:
        enabled: true
        flush_timeout: 200ms
        sizer: requests
        min_size: 100
        max_size: 1000

After

  exporters:
    splunk_hec:
      token: "..."
      endpoint: "https://splunk:8088"
      sending_queue:
        batch:
          flush_timeout: 200ms
          sizer: requests
          min_size: 100
          max_size: 1000

If you previously used batcher without an explicit sending_queue, mark the queue as blocking by setting wait_for_result to true.

  sending_queue:
    wait_for_result: true
    batch: