refactor: Add log_std(out|err) bools to repo_utils that execute a subprocess (#2817)

While making a local patch to work around #2640, I found that I had a
need for running a subprocess (`gcloud auth print-access-token`) via
`repo_utils.execute_checked_stdout`. However, doing so would log that
access token when debug logging was enabled via
`RULES_PYTHON_REPO_DEBUG=1`. This is a security concern for us, so I
hacked in an option to allow a particular `execute_(un)checked(_stdout)`
call to disable logging stdout, stderr, or both.

I figure this might be useful to others so I thought I'd upstream it.

`execute_(un)checked(_stdout)` now support `log_stdout` and `log_stderr`
bools that default to `True` (which is the same behavior as before this
PR.

When the subprocess writes to stdout and `log_stdout = False`, the
logged message will show:

```
===== stdout start =====
<log_stdout = False; skipping>
===== stdout end =====
```

If the subprocess does not write to stdout, the debug log shows the same
as before:

```
<stdout empty>
```

The above also applies for stderr, with text adjusted accordingly.