feat: add custom certificate

[matheuspolitano]

Description

https://jira.schwarz/browse/STACKITCDN-1000

Implement Certificate to CDN custom domain

relates to #1234

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• Unit tests got implemented or updated
• Acceptance tests got implemented or updated (see e.g. here)
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)

[marceljk]

Only a nitpick, but could rename plan to model.

Suggested change

	var plan CustomDomainModel
	var model CustomDomainModel

[marceljk]

When I run the acc tests, I get an error that this dns_name is already used. To avoid collisions, this should be (partly) a random name. You can create a var, which stores the dns name for the acc test run and reuse it everywhere. e.g.:

var dnsName = fmt.Sprintf("tf-acc-%s.stackit.gg", acctest.RandStringFromCharSet(5, acctest.CharSetAlpha))

[marceljk]

This step isn't needed and can be removed, because you already checked this a few lines above. Also the datasource can't perform an update, only the resource can do it. You can change the step to use configCustomDomainResources if you want, but this step is not necessary

[marceljk]

Both values should be changed to computed, since they don't need to be set for a read and it doesn't change everything.

Suggested change

	Optional: true,
	Sensitive: true,
	},
	"private_key": schema.StringAttribute{
	Description: certificateSchemaDescriptions["private_key"],
	Optional: true,
	Computed: true,
	Sensitive: true,
	},
	"private_key": schema.StringAttribute{
	Description: certificateSchemaDescriptions["private_key"],
	Computed: true,

[marceljk]

Actually, I think they both attributes can be removed, because they can't be read from the API and will always stay empty. This will probably require some adjustments, because then the datasource and resource can't share a model and the map function

[marceljk]

nitpick

Suggested change

	certificateObj, conversionDiags := types.ObjectValue(certificateTypes, certAttributes)
	diags.Append(conversionDiags...)
	if diags.HasError() {
	return core.DiagsToError(diags)
	}
	certificateObj, diags := types.ObjectValue(certificateTypes, certAttributes)
	if diags.HasError() {
	return fmt.Errorf("failed to map certificate: %w", core.DiagsToError(diags))
	}

[marceljk]

Can be removed when applying the previous change

Suggested change

var diags diag.Diagnostics

[marceljk]

Can be stored in a separate type and reuse it here.

Add this at the top of this file, next to CustomDomainModel

type CertificateModel struct {
	Certificate types.String `tfsdk:"certificate"`
	PrivateKey  types.String `tfsdk:"private_key"`
	Version     types.Int64  `tfsdk:"version"`
}

and then you can use it here

Suggested change

	var certModel struct {
	Certificate types.String `tfsdk:"certificate"`
	PrivateKey types.String `tfsdk:"private_key"`
	Version types.Int64 `tfsdk:"version"`
	}
	var certModel CertificateModel