[processing] Add algorithm to extract min/max pixel from raster

[nyalldawson]

This algorithm extracts extrema (minimum and maximum) values from a given band of the raster layer.

The output is a vector layer containing point features for the selected extrema, at the center of the associated pixel.

If multiple pixels in the raster share the minimum or maximum value, then only one of these pixels will be included in the output.

The algorithm uses raster iterator to remain efficient on huge rasters, and does not require reading the entire raster to memory

[github-actions]

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[qgis-bot]

@nyalldawson
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[qgis-bot]

@nyalldawson
A documentation ticket has been opened at qgis/QGIS-Documentation#9371
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
Thank you!