feat: Resource import into state implementation

[kklimonda-cl]

Implement terraform state importing without use of Tfid attribute, by creating provider::panos::create_import_id function that converts given object with location and name attributes into base64 encoded string that can be used as argument for terraform import command and import stanzas.

Closes: #79 #148 #149 #150

[jaspalo]

question: Would you consider rename the struct for better alignement with the purpose of the function described in the definition section of it?

[jaspalo]

suggestion: the else branch can be skipped since the previous conditional contains return. This may require to have a unique name for the error returned by resourceFuncs.CreateImportId which also eliminates need for error variable declaration.

[jaspalo]

suggestion: we may benefit from separating the successful return data from the error data here. One of the way is to have a dedicated struct as follows:

type RenderArtifacts struct {
	dataSources  []string
	resources    []string
	partialsMetadata map[string]properties.TerraformProviderSpecMetadata
}

func (c *Creator) RenderTerraformProviderFile(spec *properties.Normalization, typ properties.ResourceType) (*RenderArtifacts, error) {
    ...
}

The change can also improve the function's return statements such as return nil, nil, nil, err in several places by making the manipulation of return data more structured and convenient along the way.

[jaspalo]

suggestion(non-blocking): This and the following iota can be skipped as follows:

const (
	SchemaResource   SchemaType = iota + 1
	SchemaDataSource SchemaType 
	SchemaCommon     SchemaType
	SchemaProvider   SchemaType
)

The change may also improve the constant group's default zero-value detection since the first constant has non-zero value.