Allow replacements in url generation in add_run.py
cibuglog constructs links to the test results based on the test name and patterns given to add_run.py.
i915 gfx CI hosts test results for an IGT test of name "igt@foo/bar@quz" at URL "igt@foo_bar@quz.html" which is impossible to represent with just the url pattern {test}, as {test}.html becomes igt@foo/bar@quz.html. Allow for replacement fields in the pattern so we can properly link to all results.