Update extension action items on GitHub

Created by: AlicjaSuska

Part of the tracking issue #16165, RFC 250

Description

Updates for GitHub:

• display extension action items in the header, remove the labels
• add tooltips to action items, follow Github styles. Content of the tooltips should be the same as on Sourcegraph
• add static info to the file header, next to the information provided by GitHub
• add tooltips to the static info items that require it
• implement the behavior of dropping items to the next row for many action items/static info items
• for diffs, keep action items and static info items displayed per file

Design details

• Figma

Important note: for static action items that have no data, display 'no data' label analogically to what's in the bottom bar on Sourcegraph.