Add a feature to KubernetesResourceHandler to reuse Jinja templates

[NohaIhab]

Context

The current implementation of KubernetesResourceHandler has a limitation where using jinja's tags to reference a template from within another template, for example the include tag and the import tag.
With this limitation, we resort to duplicating files as a workaround. See an example in this pr, look at katib-config.yaml.j2 and katib-config-configmap.yaml.j2 in the katib-controller templates.

What needs to get done

1. Look into the usage of Jinja's tags
2. Implement this feature in KubernetesResourceHandler
3. Add an API in the base charm's kubernetes compontent
4. Write tests for krh and the base charm

Definition of Done

chisme's KubernetesResourceHandler and the base charm's kubernetes component allow reusing of jinja templates, tests included.

[syncronize-issues-to-jira]

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The internal ticket has been created: https://warthogs.atlassian.net/browse/KF-5441.

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