Revert "fix: make application templates namespaced (#694)"

[razvan]

This reverts commit b326be3 (pr #694) because it breaks operator upgrades.

Any remedy (workaround) involves manual intervention and/or possibly downtime.

The error when running stackablectl release upgrade dev::

Error: failed to run webhook server

Caused by:
    0: failed to update certificate
    1: conversion webhook error
    2: failed to patch CRD "sparkapptemplates.spark.stackable.tech"
    3: ApiError: [CustomResourceDefinition.apiextensions.k8s.io](http://customresourcedefinition.apiextensions.k8s.io/) "sparkapptemplates.spark.stackable.tech" is invalid: spec.scope: Invalid value: "Namespaced": field is immutable: Invalid (Status { status: Some(Failure), code: 422, message: "[CustomResourceDefinition.apiextensions.k8s.io](http://customresourcedefinition.apiextensions.k8s.io/) \"sparkapptemplates.spark.stackable.tech\" is invalid: spec.scope: Invalid value: \"Namespaced\": field is immutable", metadata: Some(ListMeta { continue_: None, remaining_item_count: None, resource_version: None, self_link: None, shard_info: None }), reason: "Invalid", details: Some(StatusDetails { name: "sparkapptemplates.spark.stackable.tech", group: "[apiextensions.k8s.io](http://apiextensions.k8s.io/)", kind: "CustomResourceDefinition", uid: "", causes: [StatusCause { reason: "FieldValueInvalid", message: "Invalid value: \"Namespaced\": field is immutable", field: "spec.scope" }], retry_after_seconds: 0 }) })
    4: [CustomResourceDefinition.apiextensions.k8s.io](http://customresourcedefinition.apiextensions.k8s.io/) "sparkapptemplates.spark.stackable.tech" is invalid: spec.scope: Invalid value: "Namespaced": field is immutable: Invalid
stream closed: EOF for stackable-operators/spark-k8s-operator-deployment-575544b9c4-rr487 (spark-k8s-operator)

✔️ Tested locally. This test (spark-history...) uses app templates:

--- PASS: kuttl (155.61s)
    --- PASS: kuttl/harness (0.00s)
        --- PASS: kuttl/harness/spark-history-server_openshift-false_spark-3.5.8_s3-use-tls-false (150.56s)
        --- PASS: kuttl/harness/spark-history-server_openshift-false_spark-3.5.8_s3-use-tls-true (155.59s)
PASS

Description

Please add a description here. This will become the commit message of the merge request later.

Definition of Done Checklist

• Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant
• Please make sure all these things are done and tick the boxes

Author

• Changes are OpenShift compatible
• CRD changes approved
• CRD documentation for all fields, following the style guide.
• Helm chart can be installed and deployed operator works
• Integration tests passed (for non trivial changes)
• Changes need to be "offline" compatible
• Links to generated (nightly) docs added
• Release note snippet added

Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
• Documentation added or updated. Follows the style guide.
• Changelog updated
• Cargo.toml only contains references to git tags (not specific commits or branches)

Acceptance

• Feature Tracker has been updated
• Proper release label has been added
• Links to generated (nightly) docs added
• Release note snippet added
• Add type/deprecation label & add to the deprecation schedule
• Add type/experimental label & add to the experimental features tracker

[NickLarsenNZ]

Restored in #720