Child tabs support: Set `openerTabId` on new tabs

**Is your feature request related to a problem? Please describe.**

When new tabs are opened by the extension, they are not linked to the originating tab due to not having the [`openerTabId` property ](https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs/create) passed to `browser.tabs.create()`.

This somewhat confuses tab management extensions such as [Tree Style Tab](https://addons.mozilla.org/en-US/firefox/addon/tree-style-tab/) causing them to possibly insert the tab into suboptimal positions.

**Describe the solution you'd like**

When opening new tabs, the `openerTabId` should preferably be set to the originating tab ID, retrieved from eg. `(await browser.tabs.query({active: true, currentWindow: true}))[0]?.id`.

**Additional context**

I'm willing to work on a pull request if this sounds fine. Hints where to modify the code are appreciated.