IsoDatastore to Storage support

[nasark]

• IsoDatastore will be modelled under Storage with STI :type => ManageIQ::Providers::Ovirt::InfraManager::IsoDatastore, therefore these changes aim to keep the iso datastore views in tact alongside the modelling change
• create and edit operations for iso datastores can be removed as this will be handled by provider refreshes moving forward
• see Subclass IsoDatastore and transfer from core manageiq-providers-ovirt#621 for more details

Depends on:

• Subclass IsoDatastore and transfer from core manageiq-providers-ovirt#621
• consolidate supported storage types manageiq#22258

TODO:

• Fix specs

@miq-bot assign @jeffibm
@miq-bot add_reviewer @agrare
@miq-bot add_labels enhancement, technical debt

[miq-bot]

Checked commit nasark@2358dd9 with ruby 2.6.10, rubocop 1.28.2, haml-lint 0.35.0, and yamllint
6 files checked, 2 offenses detected

app/helpers/pxe_helper/textual_summary.rb

• ❗ - Line 132, Col 42 - Rails/HelperInstanceVariable - Do not use instance variables in helpers.
• ❗ - Line 136, Col 43 - Rails/HelperInstanceVariable - Do not use instance variables in helpers.

[nasark]

Cross-repo tests are green (manageiq-api failures are unrelated)