GUI Configure kubeLabels for tools

[rodichenko]

It would be nice to have an ability to specify kubeLabels for tool version settings - a set of key: value.

Approach

Tool version settings page shall display controls for specifying custom kube labels in Execution environment section (after sensitive storages configuration controls). Each label consists of a key (string) and a value (string). User shall be able to add, edit or remove labels. For predefined labels ("flags", see below) GUI shall display checkboxes (before custom kube labels section); if user enables a checkbox, a true value is set for the label, otherwise label is not set at all (considered removed).

Let's introduce ui.tool.kube.labels preference (OBJECT, JSON) - an array of keys (string) - a set of predefined kube labels, e.g.

["kube_flag_1", "kube_flag_2"]