[Feature Request] Make `grub2_info.jinja` content a "common" resource

[ferricoxide]

Is your feature request related to a problem? Please describe.

With the Red Hat Enterprise Linux 9 hardening-automation, the bootloader user/password content is (currently) broken up into two findings: one at a priority of "high" (password-protecting GRUB2 menu) and one at "medium" (superuser name). To avoid pointless duplication of configuration content, copied the …/el8 hierarchy's grub2_info.jinja into the …/el9 hierarchy that will be introduced once #506 is merged. Probably want to extend that paradigm to cover EL8, as well.

Describe the solution you'd like

Consolidate the grub2_info.jinja in the already-implemented …/el8/STIGbyID/cat1/grub2_info.jinja file and the soon-to-be-implemented …/el9/RuleById/common/grub2_info.jinja content into a single file that's referenced by both the …/el8/… and …/el9/… content. This should be done by moving the grub2_info.jinja content above (or parallel to) the …/el8/… and …/el9/… content-hierarchies and then use a fetch-method similar to what's implmented in the (pending) …/el9/RuleById/high/content_rule_grub2_uefi_password.sls and …/el9/RuleById/medium/content_rule_grub2_uefi_admin_username.sls states.

Describe alternatives you've considered

Additional context