deprecate jenkins-arachni

[garethahealy]

arachni cant be updated past the current version, as it requires a RHEL9 base:

• #691

the project is also no longer active anymore:

• https://github.com/Arachni/arachni?tab=readme-ov-file#notice
• https://ecsypno.com/pages/arachni-web-application-security-scanner-framework

but is used by:

• https://rht-labs.com/enablement-docs/#/4-an-enslaved-hope/README?id=_1b-arachni-scan

[garethahealy]

@ckavili @springdo @eformat since you are the main consumers for arachni or have used it in the past. thoughts?

[eformat]

yeah - time to deprecate fully i think - since we use ACS/Stackrox nowdays

[garethahealy]

@eformat are there any other jenkins-agents you guys don't use anymore and can be deprecated?