Fix chart last modified date (metric explorer)

[jsperhac]

Description

• Change to Metric Explorer javascript updates the timestamp on the current record of the queries store when a chart is saved.
• Change to Metric Explorer controller parses the current timestamp from the request object and saves it, when saving the "query" associated with an existing chart. This step was previously missing.

Motivation and Context

Addresses xdmod6.6 bug: https://app.asana.com/0/14787510600562/335273737938313

Tests performed

Tests run by hand:

• Alter existing ME charts, check displayed timestamp before and after saving and reloading.
• Verify that no change is made to proper behavior: save existing chart under new name
• Verify that no change is made to proper behavior: create new chart

Ran all unit and integration tests

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[smgallo]

LGTM once the linter is fed and happy.