[kernel 726] fix web bot auth extension

[archandatta]

Note

Implements Chrome enterprise policy–based extension installation and updates runtime flags handling.

• Policy: add ExtensionInstallForcelist, switch ExtensionSettings to use update_url, and add ExtractExtensionIDFromUpdateXML; AddExtension now uses Chrome extension ID (from update.xml) and maintains the forcelist
• API: during upload, detect extensions needing policy, validate presence/parsability of update.xml and a .crx, and call updated policy API; only add --load-extension flags for non-policy extensions
• Server: serve update.xml/.crx via new HTTP routes (/extensions/*, /update.xml, /{filename}.crx) so Chrome can fetch them
• Docker: make /chromium/flags bind mount writable
• Tests: remove obsolete Web Bot Auth policy test

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