Set utf-8 charset for raw logs

Dependencies

• [2] CKTDT6XX Hydra::View::Plain: Explicitly set the response body.
• [3] KI423DCQ Stream logs if possible and remove size limit
• [4] 57XH5AZ3 Set utf-8 encoding on raw log pages
• [5] U2ZK6LZ7 Fix some warnings
• [6] FQAZTEK6 Don't set Expires header for logs of unfinished builds/steps
• [7] QE253KG4 * Option to show the tail of a log.

Change contents

• replacement in src/lib/Hydra/View/NixLog.pm at line 12
  [3.715]→[3.715:761](∅→∅)
  − $c->response->content_type('text/plain');
  [3.715]

  [3.761]
  + $c->response->content_type('text/plain; charset=utf-8');
• replacement in src/lib/Hydra/View/Plain.pm at line 9
  [4.40]→[4.1287:1420](∅→∅)
  − $c->response->content_encoding("utf-8");

  − $c->response->content_type('text/plain') unless $c->response->content_type() ne "";
  [4.40]

  [2.0]
  + $c->response->content_type('text/plain; charset=utf-8') unless $c->response->content_type() ne "";