chore: Use standardized version metadata across python packages

- Defining __version__ is a rejected PEP 396 standard.
- Define the version in setup.cfg like the other python packages
- Update the `update_version.sh` script to handle all the python packages the same
- For fetching the version from code, you should use importlib:
```
from importlib.metadata import version
print(version("deephaven-plugin-ui"))
```

plugins/json/setup.cfg

@@ -3,7 +3,7 @@ name = deephaven-plugin-json
 description = Deephaven Plugin for json
 long_description = file: README.md
 long_description_content_type = text/markdown
-version = attr:deephaven.plugin.json.__version__
+version = 0.0.2.dev0
 url = https://github.com/deephaven/deephaven-plugins
 project_urls =
     Source Code = https://github.com/deephaven/deephaven-plugins

plugins/json/src/deephaven/plugin/json/__init__.py

@@ -5,8 +5,6 @@
 
 from deephaven.plugin import Registration, Callback, object_type
 
-__version__ = "0.0.2.dev0"
-
 
 class Node:
     def __init__(self, object, is_ref=False, **kw) -> None:

plugins/plotly/setup.cfg

@@ -3,7 +3,7 @@ name = deephaven-plugin-plotly
 description = Deephaven Plugin for Plotly
 long_description = file: README.md
 long_description_content_type = text/markdown
-version = attr:deephaven.plugin.plotly.__version__
+version = 0.3.0.dev0
 url = https://github.com/deephaven/deephaven-plugins
 project_urls =
     Source Code = https://github.com/deephaven/deephaven-plugins

plugins/plotly/src/deephaven/plugin/plotly/__init__.py

@@ -1,8 +1,6 @@
 from deephaven.plugin import Registration, Callback
 from plotly import io as pio
 
-__version__ = "0.3.0.dev0"
-
 
 def _init_theme():
     # Set the Deephaven style globally

tools/update_version.sh

@@ -113,26 +113,8 @@ function update_file() {
 extra=
 [ "$dev" = true ] && extra=".dev0"
 case "$package" in
-        json)
-            update_file json/src/deephaven/plugin/json/__init__.py '__version__ = "' '"' "$extra"
-            ;;
-        matplotlib)
-            update_file matplotlib/setup.cfg 'version = ' '' "$extra"
-            ;;
-        plotly)
-            update_file plotly/src/deephaven/plugin/plotly/__init__.py '__version__ = "' '"' "$extra"
-            ;;
-        plotly-express)
-            update_file plotly-express/setup.cfg 'version = ' '' "$extra"
-            ;;
-        ui)
-            update_file ui/setup.cfg 'version = ' '' "$extra"
-            ;;
-        utilities)
-            update_file utilities/setup.cfg 'version = ' '' "$extra"
-            ;;
-        packaging)
-            update_file packaging/setup.cfg 'version = ' '' "$extra"
+        json | matplotlib | plotly | plotly-express | ui | utilities | packaging)
+            update_file "${package}/setup.cfg" 'version = ' '' "$extra"
             ;;
         auth-keycloak | dashboard-object-viewer | table-example)
             # Packages that don't have any Python to publish, just ignore