Writing training output to HDFS fails with 'Pathname [path] is not a valid DFS filename.'

[MarkPundurs]

Describe the bug
Writing training output to HDFS fails with 'Pathname [path] is not a valid DFS filename.'

To Reproduce
Steps to reproduce the behavior:

1. Select a dataset.
2. Click the forecast plugin.
3. Select the training option (number 1).
4. Select an HDFS connection for the metrics dataset.

Expected behavior
Plugin writes output to specified locations.

Root cause
HDFS doesn't allow colons in paths: https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/filesystem/model.html#Paths_and_Path_Elements

Suggested fix
In dss-plugin-timeseries-forecast/custom-recipes/timeseries-forecast-1-train-evaluate/recipe.py, change line 29 from
session_name = datetime.utcnow().isoformat() + "Z"
to
session_name = datetime.utcnow().isoformat().replace(':', '.') + "Z"