Disables OSSEC email for fwupd

[kushaldas]

Status

Ready for review

Description of Changes

Fixes #5835

Adds a new rules group and also the related decoder.

Changes proposed in this pull request:

Testing

• Do install from this branch to hardware
• Make sure you don't receive the ossec alerts mentioned in fwupd error in syslog, ossec alert for Focal #5835

Deployment

Any special considerations for deployment? Consider both:

1. Upgrading existing production instances.
2. New installs.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

If you made changes to securedrop-admin:

• Linting and tests (make -C admin test) pass in the admin development container

If you made changes to the system configuration:

• Configuration tests pass

If you added or removed a file deployed with the application:

• I have updated AppArmor rules to include the change

If you made non-trivial code changes:

• I have written a test plan and validated it for this PR

Choose one of the following:

• I have opened a PR in the docs repo for these changes, or will do so later
• I would appreciate help with the documentation
• These changes do not require documentation

If you added or updated a code dependency:

Choose one of the following:

• I have performed a diff review and pasted the contents to the packaging wiki
• I would like someone else to do the diff review

[emkll]

Installed the securedrop-ossec-server package on a prod install, can confirm I no longer see the alert. I've appended a commit to add a testinfra test for these new rules in 19ade45 , and rebased on latest develop. Good to merge when CI passes.