t5558: add tests for creationToken heuristic

As documented in the bundle URI design doc in 2da14fad8f (docs:
document bundle URI standard, 2022-08-09), the 'creationToken' member of
a bundle URI allows a bundle provider to specify a total order on the
bundles.

Future changes will allow the Git client to understand these members and
modify its behavior around downloading the bundles in that order. In the
meantime, create tests that add creation tokens to the bundle list. For
now, the Git client correctly ignores these unknown keys.

Create a new test helper function, test_remote_https_urls, which filters
GIT_TRACE2_EVENT output to extract a list of URLs passed to
git-remote-https child processes. This can be used to verify the order
of these requests as we implement the creationToken heuristic. For now,
we need to sort the actual output since the current client does not have
a well-defined order that it applies to the bundles.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib-functions.sh

@@ -1833,6 +1833,14 @@ test_region () {
 	return 0
 }
 
+# Given a GIT_TRACE2_EVENT log over stdin, writes to stdout a list of URLs
+# sent to git-remote-https child processes.
+test_remote_https_urls() {
+	grep -e '"event":"child_start".*"argv":\["git-remote-https",".*"\]' |
+		sed -e 's/{"event":"child_start".*"argv":\["git-remote-https","//g' \
+		    -e 's/"\]}//g'
+}
+
 # Print the destination of symlink(s) provided as arguments. Basically
 # the same as the readlink command, but it's not available everywhere.
 test_readlink () {