Route integration actions to plugins without hitting the network

[lieut-data]

DoActionRequest in the app package detects a relative URL and automatically prepends the SiteURL to free plugins from having to do this drudgery. This improves plugin compatibility in environments where the SiteURL contains a subpath, but the plugin was not written to account for same.

However, the resulting URL must still be fully resolved: e.g. the server makes an HTTP connection to http://mm.domain.com/plugins/plugin_id/path. This will fail in environments where mm.domain.com cannot be resolved, or refuses to connect due to firewall rules. This may not be the case for single server instances, but is likely in a load balancer situation where mm.domain.com points to another box that wouldn't normally be routed to from a server.

Improve DoActionRequest to route plugin requests directly to the plugin's ServeHTTP hook implementation. This should work for any plugin already using relative URLs without requiring a plugin recompilation.

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JIRA: https://mattermost.atlassian.net/browse/MM-18068

[scottleedavis]

👍 I'd like to do this!