Wiki update: Steeltoe support policy

[bart-vmware]

Updates to the Steeltoe support policy. Minor fixes in other markdown files.

The primary changes are:

• Clarified that only the latest release per major version line receives fixes.
• Releasing a new minor/patch version does not extend the support window for that major release.

This aligns with what Microsoft and most other .NET OSS projects do.

Under the old terms:

• Releasing a new minor version of Steeltoe 3.x (to fix CVEs that also introduce breaking changes) would extend the 3.x support window by another year. So as long as new CVEs are found in 3.x, it never reaches end of support.
• Every minor version of Steeltoe 3.x ever released needs to be patched each time a CVE is found, which we can't properly test because our infrastructure (Tanzu, GitHub Actions, Azure DevOps) isn't compatible with the old versions anymore.