Add units attribute for validation purposes.

Cumulative backport for custom dimension
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Adding GUI for custom raster dimensions, and handling units and unit symbols
Confine DIM_ prefix processing to core WMS handling code, so that the reader and other protocols use the original (unprefixed) dimension name.
[GEOS-5218] Allow the WMS elevation units to be editable
[GEOS-5218] set default units for elevation dimension to EPSG:5030
fix ConcurrentModificationException when removing unsupported dimensions
Adding a prefix for custom dimensions in the metadata map to avoid collisions with other params in the metadata map
[GEOS-5539] Support raster custom dimensions generated at runtime
Fixing dynamic dimension tests after changes to coverage delegate handlers
improved custom dimensions management
fixing custom dimensions management
Centralize all the parsing needed to access the grid coverage reader dimensions in a helper object
Adding a prefix for custom dimensions in the metadata map to avoid collisions with other params in the metadata map
[GEOS-5539] Support raster custom dimensions generated at runtime
improved custom dimensions management
fixing custom dimensions management
last fixes
Add support for custom dimensions.
[GEOS-5631] Build failure in wms GetFeatureInfoIntegrationTest caused by custom template leak
align to the latest version

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Tested manually and via JUNIT tests