Remove GitLab WAF related columns from database

Why are we doing this work

More information about deprecation: #271276 (closed)

We have to remove all columns that were used in GitLab WAF feature, as they are no longer used from %14.0. It is important to gradually remove these columns across multiple releases and do it according to the process described here: https://docs.gitlab.com/ee/development/what_requires_downtime.html#dropping-columns

Relevant links

• Epic
• Database guideline for dropping a column

Non-functional requirements

• [-] Documentation
• [-] Feature flag:
• [-] Performance:
• Testing:
  • Test if Ingress can be installed and is working properly,
  • Test if Fluentd can be installed and is working properly

Implementation plan

• database drop columns modsecurity_enabled, modsecurity_mode from clusters_applications_ingress table,
• database drop column waf_log_enabled from clusters_applications_fluentd,
• database remove index_clusters_applications_ingress_on_modsecurity index