[FILTER] Conditions on Custom headers

[chibenwa]

Why

The condition exists in Thunderbird:

It allows writing advanced classification (eg mailing lists? X-GitLab-Project, X-Mailgun-Sid, etc...)

Also asked by @pvi-github

How

• In org.apache.james.jmap.api.filtering.Rule add a comparator any that matches all supplied value - can then be used to see if a given header exists.
• Refactor Condition to be based on a marker interface with class for each possible condition (mimic scala sealed traits)
• Add a condition Header taking as a field the header name.
• Modify ContentMatcher in order to handle any comparator and Header. Those should be covered by JMAPFilteringTest test suite.
• Handle those elements onto RuleDTO in order to plug them onto internal storage based on eventSourcing. FilteringManagementContract shall cover this.
• Modify FilterSerializer in order to enable serialization + deserialization in JMAP. Those should be covered by tests within LinagoraFilterSetMethodContract.
• Document the TMail backend filter extension accordingly: docs/modules/ROOT/pages/tmail-backend/jmap-extensions/jmapFilters.adoc
• Create the follow up task in order to integrate that into https://github.linagora.com/linagora/tmail-flutter