doc: readme overhaul and azure sponsorship (#2826)

* new readme structure

* add adopters file

* add microsoft sponsorship

* add reference to adopter file

* add gopher slack invite link

* slightly rephrase nightly image section

* add sponsor request for action

* better formatting for contributor wall

* add longer wait time for stale PRs and issues and allow for exemption through bug and high-priority labels

* apply review suggestion

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>

---------

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>

ADOPTERS.md

@@ -0,0 +1,28 @@
+# Adopters
+
+This list showcases organizations that leverage OAuth2-Proxy within their
+infrastructure. If your organization uses OAuth2-Proxy and isn't yet listed, we
+encourage you to add it!
+
+This list aims to be a comprehensive and trusted resource for the OAuth2-Proxy
+community, demonstrating successful adoption across all kinds of industries.
+
+Contributing to this list is a simple way to impact the project's growth,
+maturity, and momentum. Thank you to all adopters and contributors of the
+OAuth2-Proxy project!
+
+## Updating this list
+
+To add your organization to this list, you can just [open a PR](https://github.com/oauth2-proxy/oauth2-proxy/pulls)
+to directly update this list.
+
+Add your organization name, your github username and if you desire a short
+description on how you utilize oauth2-proxy.
+
+## OAuth2-Proxy Adopters
+
+This list is sorted in the order that organizations were added to it.
+
+| Organization | Contact | Description of Use |
+| ------------ | ------- | ------------------ |
+|              |         |                    |