Fill in Variable Importance user guide page with info about non-tree-based models

[exalate-issue-sync]

For some reason our [Variable Importance page|http://docs.h2o.ai/h2o/latest-stable/h2o-docs/variable-importance.html] only contains information about tree-based models. We should copy the information about how varimp is calculated for all algorithms (from their individual user guide pages), so that this page can serve as a central point for all variable importance related information.

There should be a subsection for each algorithm type, which at the very least points to a varimp section on their own algorithm page (but probably better just to duplicate it here).

Note that Stacked Ensembles do not currently have variable importance available: [https://0xdata.atlassian.net/browse/PUBDEV-5137|https://0xdata.atlassian.net/browse/PUBDEV-5137|smart-link]

[h2o-ops]

JIRA Issue Migration Info

Jira Issue: PUBDEV-7822
Assignee: hannah.tillman
Reporter: Erin LeDell
State: Resolved
Fix Version: 3.32.0.3
Attachments: N/A
Development PRs: Available

Linked PRs from JIRA

#5100