Engineering: MSBuild release & version targets

Part of #1655

Initial prototype target files can be found here: https://github.com/jviau/dotnet-worker-layout/tree/main/eng/targets

We will introduce custom MSBuild targets which handle the following:

Handles targets for setting:

1. Common package/nuget settings
2. CI values
3. Versioning

## Versioning

We will adopt the following version schema: `{VersionPrefix}(-{VersionSuffix})?`, where `VersionSuffix` breaks down as: `Preview.N.BuildReason.BuildNumber.BuildRevision`

- `Preview` -> the optional preview tag we use. Typically only even `preview`, but may take on other values if we deem it necessary. This is optional and set in the csproj.
- `N` -> the preview number. Starts at `1`. Increments with each preview. This allows us the release successive previews without modifying `VersionPrefix`
- `BuildReasion` -> `dev`, `pr`, or `ci`. Dropped for release builds.
- `dev` -> always used during local builds
- `pr` -> always used for PR builds
- `ci` -> always used for non-release CI builds
- `BuildNumber` -> the date of the build in `yyMMdd` format. Dropped for release builds.
- `BuildRevision` -> the Azure pipelines build revision, an incrementing number to avoid build number conflicts from the same day. Always `0` for dev builds. Dropped for release builds.

## Release builds

Release build versions are triggered by building from a tag. The format must match `v.*`, or `{ext}-v.*`, where {ext} is an approved extension section being released. When a CI build is triggered from a tag, the additional version suffix from above is dropped (BuildReason.BuildNumber.BuildRevision).

examples:

- Local build: (preview) `1.0.0-preview.1.dev.230712.0`, (non-preview) `1.0.0-dev.230712.0`
- PR build: (preview) `1.0.0-preview.1.pr.230712.1`, (non-preview) `1.0.0-pr.230712.1`
- CI build: (preview) `1.0.0-preview.1.ci.230712.1`, (non-preview) `1.0.0-ci.230712.1`
- Release build: (preview) `1.0.0-preview.1`, (non-preview) `1.0.0`

## Package contents

All packages will now have their own `readme.md` and `release_notes.md`. Both of which will be pulled into the nuget package.

### README

The per-package readme.md is copied into the nuget package. The contents of this readme should include:

1. Brief overview of the package
1. Commonly used types, if applicable
1. A getting started section, if applicable

### Release Notes

The per-package release_notes.md contents will be copied into the package. They will also be prefixed with `See $(RepositoryUrl)/releases/tag/$(ReleaseTag)`, giving a link back to our Github release for further details.

The per-package release notes should cover only the changes made to this package in this release, being reset after every release.