fix: Work around 'unreliable' input data for Registry modules

[radeksimko]

As discovered in hashicorp/vscode-terraform#1582 it turns out that we assume inputs in some modules as required, when they are actually not.

• Why? - Because we use data from the Registry API, which (incorrectly) indicates some inputs as required.
• Which ones? - Modules which have "nullable" inputs (variables with default = null)
• Why? - Because the Registry API did not recognise "nullable" inputs at the time of ingesting the module.
• Can't the Registry fix this? - The Registry already recognises "nullable" inputs since 19th August 2022.
• Can't the Registry fix the data then? - This was considered but it involves potentially a lot of modules and module versions, so this is a non-trivial task, esp. given that this would involve basically re-ingesting the modules/versions.

So this ^ is why we're taking a more pragmatic approach and basically treat any required inputs as optional for any modules which we know were published prior to the date when the Registry implemented support for "nullable" inputs.

Importantly, this does not impact recently published modules and module versions. Those will continue to have inputs reflected as-is.

[dbanck]

Looks like a good pragmatic solution to me

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