fix: small fixes around input DA variables

[akocbek]

Description

Issue: #297

• existing_kms_key_crn is currently in the required list but should be moved to optiona
• move use_existing_resource_group next to resource_group_name in ui (on required).
• elser_model_type -> this is only applicable if plan is platinum (not for enterprise). At minumum indicate it in the description of the variable.
• skip_es_sm_auth_policy -> use full service name when they are not obvious to typical end-user (skip_elastic_search_secret_manager_auth_policy or skip_elastic_search_to_secret_manager_auth_policy)
• existing_db_instance_crn -> use elastic_search instead of db for consistency in naming.
• skip_iam_authorization_policy and skip_es_sm_auth_policy are inconsistent in term of naming.
• group related inputs together in ui - eg: all kms related input together.

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[akocbek]

/run pipeline