Adding hvplot backend testing (#189)

## Description

Adding new test config files for the hvplot backend

src/eva/tests/config/testGsiObsSpaceAmsuaMetop-A_hvplot.yaml

@@ -0,0 +1,94 @@
+datasets:
+  - name: experiment
+    type: GsiObsSpace
+    satellite: metop-a
+    sensor: amsua
+    filenames:
+      - ${data_input_path}/gsi_obs_space.amsua_metop-a_ges.2020092200.nc4
+    channels: &channels 3,8
+    groups:
+      - name: GsiNcDiag
+        # Note: channelNumber is automatically added to the output and should not
+        # be listed as a variable
+        variables: &variables [Obs_Minus_Forecast_adjusted,
+                               Observation,
+                               Latitude,
+                               Longitude]
+
+transforms:
+  # Stats for hofxPassedGSIQc
+  - transform: channel_stats
+    variable_name: experiment::GsiNcDiag::${variable}
+    for:
+      variable: *variables
+
+graphics:
+
+  plotting_backend: Hvplot
+  figure_list:
+
+  # Histogram plots
+  # ---------------
+
+  # OmB Jedi and OmB GSI
+  - batch figure:
+      variables: Obs_Minus_Forecast_adjusted
+      channels: *channels
+    figure:
+      layout: [1,1]
+      title: 'GSI omf | AMSU-A Metop-A | Omf'
+      output name: histograms/amsua_n19/Obs_Minus_Forecast_adjusted/${channel}/gsi_omb_histogram_amsua_n19_Obs_Minus_Forecast_adjusted_${channel}.html
+    plots:
+      - add_xlabel: 'Observation minus forecast'
+        add_ylabel: 'Count'
+        add_legend:
+          loc: 'upper left'
+        statistics:
+          fields:
+            - field_name: experiment::GsiNcDiag::Obs_Minus_Forecast_adjusted
+              channel: ${channel}
+              xloc: 0.5
+              yloc: -0.10
+              kwargs:
+                color: 'black'
+                fontsize: 8
+                fontfamily: monospace
+          statistics_variables:
+          - n
+          - min
+          - mean
+          - max
+          - std
+        layers:
+        - type: Histogram
+          data:
+            variable: experiment::GsiNcDiag::Obs_Minus_Forecast_adjusted
+            channel: ${channel}
+          color: 'blue'
+          label: 'GSI omb (all obs)'
+          bins: 100
+          alpha: 0.5
+
+  # ---------- Statistical Plot ----------
+  # JEDI h(x) vs GSI h(x)
+  # -------------------------
+  - figure:
+      layout: [1,1]
+      title: 'Mean HofX vs Channel'
+      output name: hofx_vs_channel/amsua_n19/brightness_temperature/meanhofx_vs_channel.html
+    plots:
+      - add_xlabel: 'Channel'
+        add_ylabel: 'GSI HofX'
+        add_grid:
+        add_legend:
+          loc: 'upper left'
+        layers:
+        - type: Scatter
+          x:
+            variable: experiment::GsiNcDiag::channelNumber
+          y:
+            variable: experiment::GsiNcDiagMean::Obs_Minus_Forecast_adjusted
+          markersize: 5
+          color: 'red'
+          label: 'GSI h(x) versus channels (all obs)'
+          do_linear_regression: False