US-613462 Support adding WEB_XML_SNIPPET

[maracle6]

This is a proposed solution for US-613462 and https://github.com/pegasystems/pega-helm-charts/issues/577 which allows a user of the pega Helm chart to define an env variable WEB_XML_SNIPPET which will be inserted into the web.xml just before the tag. This allows users to: Add an additional servlet Add a security constraint Add JMS resources

Without the snippet feature, the user needs to either embed an entire 1600+ line web.xml into their values file, or put a replacement web.xml into the config/deploy folder (which either means using local charts instead of hosting in a repository, or having to repackage every chart release with the customization).

This feature also pairs with the existing functionality we have for specifying a CONTEXT_XML_SNIPPET.