fix(iOS): change hardcoded config path when using custom config file for auto register plugins

[tossaro]

When I use InstanceDescriptor with custom config path, the CapacitorBridge initialization on the CAPBridgeViewController is by default autoRegisterPlugins set to true.
But as we can see on CapacitorBridge class function registerPlugins config path is hardcoded
if autoRegisterPlugins { do { if let pluginJSON = Bundle.main.url(forResource: "capacitor.config", withExtension: "json") { //..
So, I've created new property configUrl that will be given when parsing configuration at InstanceDescriptor initialization.

[eric-horodyski]

Thanks for opening this PR 🙏

As part of our backlog maintenance effort, we’re reviewing older pull requests for compatibility with the current branch structure and latest releases.

Details: https://ionic.io/blog/keeping-capacitors-backlog-healthy

This PR will need to be rebased against the latest main branch and updated to resolve merge conflicts.

If we don’t see updates within 7 days, we’ll close it to keep the queue focused — but it can always be resubmitted once updated.