Add support policy

SUPPORT_POLICY.adoc

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+= Spring Authorization Server Support Policy
+
+The Spring Authorization Server support offering provides the following support terms:
+
+* Releases are currently in the format of 0.x.y, where:
+** “x” contains new features and potentially breaking changes.
+** “y” contains new features and bug fixes and provides backward compatibility.
+* The Spring Authorization Server project will be supported for at least 3 years after the most recent 0.x.0 release is made available for download.
+* Security fixes will be provided for at least one year after the 0.x.0 release is made available for download. Security fixes will not be provided for updating versions to third-party libraries.
+* Feature support and bug fixes, excluding “Security fixes”, will be provided only for the latest 0.x.y release.
+* This support policy starts with version 0.2.0.
+* We will switch to the standard https://tanzu.vmware.com/support/oss[Spring OSS support policy] when the Spring Authorization Server project reaches version 1.0.0.
+
+An example can help us understand all of these points.
+Assume that 0.2.0 is released in August of 2021.
+This means that the Spring Authorization Server project is supported until at least August of 2024.
+If 0.3.0 is then released in May of 2022, the Spring Authorization Server project is supported until at least May of 2025.
+The 0.3.0 release may contain breaking changes from 0.2.0.
+If a bug is found, only 0.3.0 will be patched in a 0.3.1 release.
+If a security vulnerability is found, a 0.2.4 (assume 0.2.3 is latest) and 0.3.1 release will be provided to fix the security vulnerability.
+However, a vulnerability found in September of 2022 would be fixed in the 0.3.1 release but not the 0.2.3 release, because the vulnerability was discovered more than a year after the 0.2.0 release date.