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[ZBXNEXT-8907] added API changes for pie chart and graph widget legend

* commit '3623cec1a7b6fc1fa61e185763219fe6f186c2fd':
  [ZBXNEXT-8907] changed link in API changes for new field in graph
  [ZBXNEXT-8907] added line break to pie chart legend legend_lines_mode parameter name
  [ZBXNEXT-8907] added line break to graph legend legend_lines_mode parameter naming
  [ZBXNEXT-8907] fixed API changes, graph legend parameters and pie chart legend parameters
  [ZBXNEXT-8907] added API changes for Pie chart and graph widget legend