fix: esa_enabled for r/vcf_instance

[spacegospod]

Summary of Pull Request

Support for configuring vSAN in ESA mode was added in VCF 5.
It was implemented as an optional attribute with #190

The flaw in my original PR is that the new property is optional and since it is marked with "omitempty" it is skipped during serialization whenever it is set to false.

I've made a change to the SDK that marks the property as required. The containing structure is still optional.

This means that esa_enabled will now behave as follows:

• When esa_enabled = true the VSANEsaConfig structure will be set and vSAN will be configured in ESA mode
• When esa_enabled = false the VSANEsaConfig structure will be set and vSAN will be configured in normal mode
• When esa_enabled is not set the VSANEsaConfig structure will be set and vSAN will be configured in normal mode

This will ensure that

1. ESA is optonal
2. The default mode is non-ESA

Type of Pull Request

• This is a bug fix.
• This is an enhancement or feature.
• This is a code style/formatting update.
• This is a documentation update.
• This is a refactoring update.
• This is a chore update
• This is something else.
  Please describe:

Related to Existing Issues

Closes #217

Test and Documentation Coverage

Ran TestAccResourceVcfSddcBasic by modifying the configuration for the 3 scenarios listed above - esa_enabled set to true, false and to nothing.

For bug fixes or features:

• Tests have been completed.
• Documentation has been added/updated.

Breaking Changes?

• Yes, there are breaking changes.
• No, there are no breaking changes.

[github-actions]

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