Add --start and --end to elastalert-test-rule

[pboushy]

The main elastalert command has a --start and --end that are really helpful for testing frequency rules.

It would be great if elastalert-test-rule had the same capability.

[jertel]

Per the usage it does have the same capability. Are you seeing otherwise?

$ elastalert-test-rule 
usage: elastalert-test-rule [-h] [--schema-only] [--days DAYS] [--start START] [--end END] [--stop-error] [--formatted-output] [--data FILENAME] [--alert] [--save-json FILENAME] [--use-downloaded] [--max-query-size MAX_QUERY_SIZE]
                            [--count-only] [--config CONFIG]
                            rule
elastalert-test-rule: error: the following arguments are required: rule

[pboushy]

You're right, it does exist...

I didn't check the command help because I read this in [the documentation] (https://elastalert2.readthedocs.io/en/latest/ruletypes.html#testing) (emphasis mine):

--days N: Instead of the default 1 day, query N days. For selecting more specific time ranges, you must run ElastAlert 2 itself and use --start and --end.

Maybe I should submit feature requests after getting some sleep.

I'll submit a PR to modify that to say "For selecting more specific time ranges, use --start and --end."