Add metric selector to performance data graph tab

[gdm-maha]

Summary:

This change adds a collapsible metric selector to the IcingaDB performance data graph tab so users can choose which perfdata metrics to display instead of always showing all metrics

Changes:

New file library Perfdatagraphs Widget MetricSelector.php. New MetricSelector widget that renders a CSS only collapsible dropdown with one checkbox for each available metric. Uses GET form submission so IcingaWeb2 handles navigation normally without custom ajax handling

Adds perfdatagraphs.noselector=1 to submitted URLs so dashboard tiles can suppress the selector and show only the chart

Parses perfdatagraphs label with support for both repeated parameters and comma separated values used by dashboard tile links, maybe we only want one as they do the same thing.

Collects available metric labels from response datasets. Shows the metric selector only when datasets are available and noselector is not enabled, might want to add default behavior when only one metric is available.

Updated file public css module.less:
Adds styling for the metric selector to better match the IcingaWeb2 look. Uses CSS only open and close behavior through checked sibling selectors.

Adds custom checkbox styling and selected state highlighting.

Updated file public js module.js:
Adds shift click range selection for metric checkboxes, some JS was needed for this to work.
Closes the selector flyout on rendered when metrics are already selected so ajax navigation does not leave it open

[martialblog]

Hi, before we dive into implementations I want to think a bit about what a good solution might look like. I want to be very deliberate when introducing new features and especially UI deliberate.

I opened an issue for discussing this #101