Implement Upsert Metric Modal for Experiments v2

[zackcl]

Resolves #2631

@danoswaltCL I've opened this new PR since the old PR #2648 had too many conflicts with the latest experiment-design-refresh branch. I've applied all the changes in #2648 in this PR and then made these further changes:

• Filtered out all reward metric options in the Metric ID field. (Needs confirmation - let me know if the reward metric key of the current experiment should remain visible.) (fixes the comment)
• Disallowed editing and deleting reward metrics.
• Added validation requiring metric class, key, and ID selection from the provided options, with cascading field clearing. (fixes the comment)
• Prevented the Save button from being incorrectly enabled in edit mode for categorical metrics. (fixes the comment)
• Applied the appTrimInput directive to all input fields in UpsertMetricModalComponent.

Here are some of your comments that are unresolved and needs discussion:

• Need extra top/bottom paddings for the inner scrollable content in the modal (comment) Dan: disregard
• The "Description" field is missing from the submitted request. Do we even store this in the DB? If not, should we remove this field from the modal? (comment) Dan: this can be removed
• Maybe this modal needs a speedbump (comment) Dan: disregard, not needed!
• Maybe we should improve the display of the Metrics table ([comment] (Implement Upsert Metric Modal for Experiments #2648 (comment))) Dan: this should be a new story for later, @zackcl maybe some draft design ticket?