Restore mlir-opt `--run-reproducer` option to opt-in running a reproducer

When tooling out there produces a reproducer that is archived, the first thing
a user is likely to expect is to process this as they do with any MLIR file.
However https://reviews.llvm.org/D126447 changed the behavior of mlir-opt to
eliminate the `--run-reproducer` option and instead automatically run it when
present in the input file. This creates a discrepancy in how mlir-opt behaves
when fed with an input file, and is surprising for users.
The explicit passing of `--run-reproducer` to express user-intent seems more
in line with what is expected from `mlir-opt`.

Reviewed By: rriddle, jpienaar

Differential Revision: https://reviews.llvm.org/D149820