Related to https://github.com/fleetdm/fleet/issues/5504, this change attempts to improve the output of the `fleetctl debug errors` command by:
- Adding a warning message to redact sensitive data
- Adding a `json` extension to the output file
- Allowing to stream the output to stdout via the `-stdout` flag or the `STDOUT` env var
The output after this changes is:
```
~/projects/fleet $ ./build/fleetctl debug errors
################################################################################
# WARNING:
# The generated file may contain sensitive data.
# Please review the file before sharing.
#
# Output written to: fleet-errors-2022-05-05T12:46:42-03:00.json
################################################################################
```
It also modifies the output of `fleetctl debug archive`
```
################################################################################
# WARNING:
# The files in the generated archive may contain sensitive data.
# Please review them before sharing.
#
# Archive written to: fleet-profiles-archive-2022-05-05T12:46:59-03:00.tar.gz
################################################################################
```
