Update doc and validation of HPCS backup encryption keys

[dishankkalra23]

Description

1. Update the description and add validation for KP and HPCS in the backup_encryption_key_crn variable
2. Removes validation for kms_key_crn when backup_encryption_key_crn is not available in the main configuration of the module

GE Issue - https://github.ibm.com/GoldenEye/issues/issues/9359

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Release notes content

Enhancements:

1. Updated description and Validation for the backup_encryption_key_crn variable to ensure both Key Protect and HPCS keys follow the proper format.
2. Updated validation logic for the backup_encryption_key_crn in the main configuration. If no value is provided, the module will now default to using kms_key_crn for both Key Protect and HPCS as the backup encryption key.
3. Updated the FSCloud submodule and its associated example to integrate the use of HPCS keys for backup encryption.

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[dishankkalra23]

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🎉 This PR is included in version 3.14.3 🎉

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