Readme templates should automatically determine support status from version

See https://github.com/dotnet/dotnet-docker/pull/6762#pullrequestreview-3384970245

The support status of various .NET releases is listed in the featured tags section of each repo's README: https://github.com/dotnet/dotnet-docker/blob/2a6f35b9361d1aacb664b0ce09e529698b622d2b/README.sdk.md?plain=1#L3-L10

That status is hard-coded in the following template:

https://github.com/dotnet/dotnet-docker/blob/2a6f35b9361d1aacb664b0ce09e529698b622d2b/eng/readme-templates/FeaturedTags.md

However, we could compute it automatically. The following logic would work for this (pseudocode):

```
if build version contains "alpha" -> "(Alpha)"
if build version contains "preview" -> "(Preview)"
if build version contains "rc" -> "(Release Candidate)"
else ->
if major version is even -> "(Long-Term Support)"
else -> "(Standard Support)"
```