Allow deployment slot settings

[nargiz]

This PR closes #838

The changes in this PR are as follows:

• Allows you to specify slot settings for web app/functions using slot_setting and slot_settings

I have read the contributing guidelines and have completed the following:

• [x] Tested my code end-to-end against a live Azure subscription.
• [x] Updated the documentation in the docs folder for the affected changes.
• [x] Written unit tests against the modified code that I have made.
• [x] Updated the release notes with a new entry for this PR.
• [x] Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

let myWebApp = webApp {
    name "test"
    add_slot deploymentSlot

    slot_settings ["my_slot_setting", "sticky value"]
}

[r30e]

@isaacabraham this is the only open issue with slots that I'm aware of. How would you propose this is achieved without the additional keyword? I can imagine a solution using a single-case-DU to tag a value as SlotSticky but I'm not sure this would be clearer?

[isaacabraham]

@nargiz I'm really sorry this hasn't been looked at for such a long time. We need to get this reviewed and merged in before it drifts too far from the main code base. @TheRSP @ninjarobot what do you both think about this - are there outstanding review issues that need to be resolved?

[ninjarobot]

I have some comments in the PR just around aligning with the existing DSL and making this fit with the concepts that are already there. It could be my misunderstanding of the intention, but I want to prevent DSL sprawl.

[nargiz]

Sorry, I got a bit confused with the DSL requirements, how slot_settings should be named/represented and distracted with other things. Thanks for reminding me. I will check it by the end of the week.

[martinbryant]

Hi @nargiz - can we look at getting the conflicts dealt with so it can be reviewed? Thanks