20219: Replace API & websocket log loading with webdav polling

20219: Replace API & websocket log loading with webdav polling

* Add apiWebdavClient to log service for making webdav requests to the API and
  differentiate from keepWebdavClient
* Add listLogFiles and getLogFileContents methods to log service, contents can
  be fetched with range request
* Add loadContainerLogFileContents to load logs using webdav range requests
  * Files larger than the chunk limit (128k) are loaded as beginning and end
    in 2 64k fragments, snipline is appended to the last line of the first
    fragment
  * The chunks are all requested in parallel
* Add sorting of timestamped log types in combined log views (Main/All)
  * Lines without timestamps are merged with previous lines with timestamps
    * If no preceding lines of a sortable type exist, the leading lines are
      removed from combined log views - they can still be seen in the single
      log type filter
  * Non-timestamped log types (node-info/contaner) are pushed to the bottom
    with original ordering in All view
  * Merging & sorting is not applied to single log type view
* Remove snipline LogEventType as all sniplines now belong to specific log
  event types
* Update logs panel store and reducer to remember the last log byte requested
* Add polling useAsyncInterval utility function to poll log file sizes
  * Polling awaits for callback to finish to prevent race conditions
* Update process log code snippet style to remove gap between array of loglines
* Remove websocket handling of log events
* Replaced cypress log manipulation commands with webdav log helpers
* Add tests for polling, line sorting, correctly sized/positioned chunks, and
  snipline

Arvados-DCO-1.1-Signed-off-by: Stephen Smith <stephen@curii.com>