Add new getting started step for starter policies

[shaun-od]

Background

Platform Hub policies getting started docs need to be updated with the starter policies feature.

Result
Updates the getting started guide with starter policy details.

To be merged once Starter Policies name has been confirmed

[steve-fenton-octopus]

LGTM!

[octo-ryanhall]

Suggested change

	- If you want to start with the most basic policy, choose Create Blank Policy.
	If you want to start with the most basic policy, choose Create Blank Policy.

@shaun-od did you mean to add this as a bullet point?

[octo-ryanhall]

Suggested change

	The slug can not be changed once a policy is created.

@shaun-od another bullet point which I am not sure if it's intentional

[octo-ryanhall]

@shaun-od I realise this change is not included in this PR but I spotted it and it looks like a copy error and not required

[octo-ryanhall]

Suggested change

You’ll now need to define the policy's scope, as Rego in the OCL file. Octopus will provide data about your deployments to the policy engine to use during evaluation. When you are writing your Rego code for scoping or conditions, this input data is available under the value ```input.VALUE```. This scope section of the policy defines the package name, which must match the underlying .ocl file name the policy is stored in. By default, the policy evaluates to false. The scope will evaluate to true if the deployment is going to the Production environment, for the ACME project, and in the Default space - all three conditions must be true at the same time.

You’ll now need to define the policy's scope, as Rego. Octopus will provide data about your deployments to the policy engine to use during evaluation. When you are writing your Rego code for scoping or conditions, this input data is available under the value ```input.VALUE```. This scope section of the policy defines the package name, which must match the underlying .ocl file name the policy is stored in. By default, the policy evaluates to false. The scope will evaluate to true if the deployment is going to the Production environment, for the ACME project, and in the Default space - all three conditions must be true at the same time.

@shaun-od we should drop the mention of the OCL file because all policy changes are being made in the UI and not as code.

[octo-ryanhall]

@shaun-od do we need to callout that ēvaluate is a required keyword and cannot be renamed?

For conditions we call out the following:
You cannot rename result, it must be called result.

[octo-ryanhall]

@shaun-od I've added a couple of suggestions that require a review before we publish the docs. I think we have a few things we need to also consider.

Should we update the code snippets in these docs so that they reflect the code in the starter policies? Currently they are missing the comments.