add `EscalationChainRef` and `EscalationChainSelector` fields to `oncall.grafana.crossplane.io.Integration` resource

[joeyorlando]

Description of your changes

Closes https://github.com/grafana/oncall/issues/4411

I have:

• [x] Read and followed Crossplane's [contribution process].
• [ ] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

Still a WIP.. still trying to get make generate to work locally to be able to test things on my local k8s cluster

[joeyorlando]

TODO

Add selector and ref fields for the following Grafana OnCall resources:

• [ ] Integration (check that there are no other related fields)
• [ ] Schedule
• [ ] Route
• [ ] Escalation

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 193 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@f68e88f). Learn more about missing BASE report.

Files	Patch %	Lines
apis/oncall/v1alpha1/zz_generated.resolvers.go	0.00%	129 Missing :warning:
apis/oncall/v1alpha1/zz_generated.deepcopy.go	0.00%	64 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #158 +/- ## ====================================== Coverage ? 0.00% ====================================== Files ? 201 Lines ? 29392 Branches ? 0 ====================================== Hits ? 0 Misses ? 29392 Partials ? 0 ``` | [Flag](https://app.codecov.io/gh/grafana/crossplane-provider-grafana/pull/158/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=grafana) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/grafana/crossplane-provider-grafana/pull/158/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=grafana) | `0.00% <0.00%> (?)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=grafana#carryforward-flags-in-the-pull-request-comment) to find out more.

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