helm: Re-factor the way we handle CRDs in fluent-operator's helm chart(s)

### Is your feature request related to a problem? Please describe.

How we currently handle CRDs:

* We currently distribute fluent-operator's CRDs in two separate "sub-charts" which are [dependencies](https://github.com/fluent/fluent-operator/tree/master/charts/fluent-operator/charts) of the "main" chart.
* This makes it difficult to upgrade Helm releases when there are CRD changes, because CRDs (in `crds/` directories) are not upgraded by default in Helm. Users have to manually fetch CRDs, run `kubectl replace` etc
* The usage of `file://` references in dependencies also causes duplicate CRDs in the release as reported [here](https://github.com/fluent/fluent-operator/issues/1709).

### Describe the solution you'd like

I'd like to propose that we implement something similar to how [Karpenter](https://github.com/aws/karpenter-provider-aws/tree/main/charts) handles their Helm releases:

* Include the `fluentd` and `fluent-bit` CRDs in the fluent-operator's "main" chart's `crds/` folder.
This will ensure all CRDs get installed during an initial helm install
* Create a new "top-level" chart named `fluent-operator-crds`
* Put CRDs in the `templates/` directory of the `fluent-operator-crds` chart
* Placing them in the `templates/` directory will allow a user to helm upgrade the `fluent-operator-crds` chart to upgrade our CRDs instead instead of having to fetch them manually and `kubectl replace` etc
* In this setup, we'll need to publish updated CRDs to two locations -- `charts/fluent-operator/crds` and `charts/fluent-operator-crds/templates` -- but this should be fairly simple with CI. (edited)

### Additional context

I don't think this would introduce any breaking changes:
* Currently, if a user wants to install fluent-operator without any CRDs, they can set `fluentd.crdsEnable` or `fluentbit.crdsEnable` to false
* Moving forward, we would deprecate these two values, and a user could simply use helm install --skip-crds` if they want to prevent CRD installation

As part of this, we can also clarify and update our documentation for "installing" and "upgrading."