Add --repeat command line argument

Google Test, for all of its painpoints, has a few features that Catch2 does not. One of them is the `--gtest_repeat` command line argument that lets you run a given configuration of tests N times (where N may also be some sentinel value for "infinite"). I would love to have this feature in Catch2. Yes, I can write a script that does it, but it is much easier if it is native to the command line tool so that I can easily repeat whatever combination and configuration of tests that I want without mucking around with external scripts.

One of the motivating use cases for this is to identify and/or reproduce spuriously failing tests.

The issue names no files or tests. Start by locating Catch2's command-line parsing and test execution entry points, then compare the requested behavior with Google Test's --gtest_repeat semantics, including the infinite sentinel. Done means selected tests can be rerun the requested number of times from the command line and flaky failures can be reproduced.

Written by the indexing model from the issue text.