feat: add microsoft strategy

[MikaelFangel]

I use ash_authentication for my Phoenix projects, and I really like it. I couldn't see a Microsoft strategy, so I thought I would add one and I hope this is a welcome improvement. I've made the tutorial and DSL so it's quite similar to other strategies.

There were a few catches:

• It was needed to remove the form_post response mode to avoid triggering the CSRF in the default browser pipeline from Phoenix.
• I couldn't find a clean way to use tenant_id directly because the discovery endpoint path is either /common/v2.0 or /{tenant_id}/v2.0 depending on your app registration, so I opted for allowing the user to override with the full base_url instead.

[jimsynz]

Thanks for putting this together! A Microsoft strategy is something we've been wanting — really keen to get this merged. I'll do a code review shortly.

[MikaelFangel]

I had some issues with multi-tenancy I'm adding the fix/feat shortly (:

[MikaelFangel]

Fixed the credo --strict software design issue and added a license file for the DSL doc. I had missed that you needed to add one together with the Spark generated file.

[jimsynz]

Nice work — this follows the same pattern as the other wrapper strategies and the multi-tenant issuer handling is well thought out. Just two small things to address before merging.

[jimsynz]