feat: support additional management policy combination

[man-ish-k]

Description of your changes

Add two new management policy combinations to support safer resource importing and external lifecycle management scenarios:

1. Import Mode: A new policy combination that allows safe importing of existing resources by only permitting observation and late initialization, without making any changes to the external resource.

   • Actions: [Observe, LateInitialize]
   • Use case: Safely discover and import existing cloud resources into Crossplane without risk of modifying them

2. External Lifecycle Management: A policy combination for resources whose lifecycle (creation/deletion) is managed outside of Crossplane, but allows Crossplane to make updates and track state.

   • Actions: [Observe, Update, LateInitialize]
   • Use case: Integration with external provisioning systems while maintaining Crossplane's ability to manage resource configuration

Fixes #681,

I have:

• Read and followed Crossplane's contribution process.
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• Added or updated unit tests.
• Linked a PR or a docs tracking issue to document this change.
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[jake-ciolek]

Hi @jbw976 and @negz . Could you please have a look at this one? It's been open for a while. Thanks!

[lsviben]

Firstly, sorry for waiting that long for a review, this slipped my mind and I got reminded just recently 🙏 .

The policies added make sense to me.

We need to add the unit tests in the right place to check the reconciler flow with the new policies.

[lsviben]

Looks good! Thanks @man-ish-k ! 🎉