Bump version to 0.69.0

[imaNNeo]

• BUGFIX (by @imaNNeo) Fix a memory leak issue in the axis-based charts, there was a logic to calculate and cache the minX, maxX, minY and maxY properties to reduce the computation cost. But it caused some memory issues, as we don't have a quick solution for this, we disabled the caching logic for now, later we can move the calculation logic to the render objects to keep and update them only when the data is changed, Memory leaking with changing spot list #1106, Improve performance on calculating minX, maxX, minY and maxY in axis-based charts #1693
• BUGFIX (by @imaNNeo) Fix showing grid lines even when there is no line to show in the LineChart, Adding more lines to the same chart panel in realtime? #1691
• IMPROVEMENT (by @sczesla) Allow users to control minIncluded and maxIncluded using SideTitles, FlTitlesData -> leftTitles shows static highest value with overlap on other titles #906
• IMPROVEMENT (by @elizabethzhenliu) Reverse the touch order in ScatterChart, so now the top spots are touched first, fixed touch detection to select topmost scatterspot  #1675
• IMPROVEMENT (by @ksw2000) Remove redundant math import, Remove redundant import of 'dart:math' #1683
• IMPROVEMENT (by @Neer-Pathak) Fix linux example build issue, fix: example app build for Linux (Issue #1667) #1668
• IMPROVEMENT (by @TobiasRump) Update the bar chart documentation, Update bar_chart.md to fix #1608 #1662