We had to introduce a web page to bootstrap the web version of devtools
because since https://bugs.chromium.org/p/chromium/issues/detail?id=1232509
chrome debugger port no longer serve such a page via HTTP.

The URL also changed, /serve_file/@{version_hash}. pattern is no longer
used, both the devtools and the websocket endpoint are in /devtools

The test was made a bit more complete by actually making requests and
trying to connect to websocket endpoints.

Some problems were found with incognito and block-new-web-contents
options:
 - they are boolean type, but the software parameter serialisation is
 XML, which as of today does not support boolean types. This is left
 TODO for now
 - When both --incognito and --block-new-web-contents are true, the
 command line flag was --incognito--block-new-web-contents, which is
 unknown and was ignored. Some minmal changes are included to fix this.

as a result, this checkout was not pinned and software was not
reproducible

This was using master branch and when it got renamed to main this
stopped working and we realized that the revision was not pinned.