cli: Let Python pick number of signing threads

This number does affect the number of concurrent rekor POST requests
we have in flight, but we are unlikely to hit rate limits as
they are defined in "requests from same host per minute".

Signed-off-by: Jussi Kukkonen <[email protected]>

Author: jku

sigstore/_cli.py

@@ -728,7 +728,7 @@ def _sign_common(
 
         # sign in threads: this is relevant for especially Rekor v2 as otherwise we wait
         # for log inclusion for each signature separately
-        with futures.ThreadPoolExecutor(max_workers=10) as executor:
+        with futures.ThreadPoolExecutor() as executor:
             jobs = [
                 executor.submit(
                     _sign_file_threaded,