Update IRIS and GELF alerter and tests

[malinkinsa]

Description

#1317 iris_ca_cert discussion

Checklist

• I have reviewed the contributing guidelines.
• I have included unit tests for my changes or additions.
• I have successfully run make test-docker with my changes.
• I have manually tested all relevant modes of the change in this PR.
• I have updated the documentation.
• I have updated the changelog.

[nsano-rururu]

Please update the documentation. The default value for gelf_http_ignore_ssl_errors has been omitted, so please correct it accordingly.

https://github.com/jertel/elastalert2/blob/master/docs/source/ruletypes.rst#iris

iris_ca_cert: Path to custom CA certificate.
↓
iris_ca_cert: Set this option to True or a path to a CA cert bundle or directory (eg: /etc/ssl/certs/ca-certificates.crt) to validate the SSL certificate.The default value is: False.

https://github.com/jertel/elastalert2/blob/master/docs/source/ruletypes.rst#graylog-gelf

gelf_http_ignore_ssl_errors: Ignore ssl error. (Only used if gelf_type=http)
↓
gelf_http_ignore_ssl_errors: Ignore ssl error. (Only used if gelf_type=http).The default value is: False.

gelf_ca_cert: Path to custom CA certificate.
↓
gelf_ca_cert: Set this option to True or a path to a CA cert bundle or directory (eg: /etc/ssl/certs/ca-certificates.crt) to validate the SSL certificate.The default value is: False.

[nsano-rururu]

@jertel
I have nothing more to point out. If there is no problem, please merge.