Rebase and cleanup the PR

Update CHANGELOG

Add changelog entries for Polly 8.3.1.

Update docs banners

Remove banners about upcoming features.

Co-Authored-By: peter-csala <[email protected]>

Add alt text to logo

Add alt text to .NET Foundation logo to resolve MD045 warning.

Add support for .NET 8 (App-vNext#1144)

- Add `net8.0` targets.
- Use .NET `TimeProvider` implementation.
- Use `FakeTimeProvider` for tests.
- Use new .NET 8 APIs where relevant.

Co-Authored-By: martintmk <[email protected]>

Use fork of AuthenticodeLint to fix validation

Use fork of vcsjones/AuthenticodeLint that is compiled against vcsjones/AuthenticodeExaminer from source to resolve issues with validating Authenticode signatures of the DLLs.

Update CHANGELOG

Add this PR to the changelog.

Delay pipeline disposal when still in use (App-vNext#1579)

Clean duplications around disposing the pipelines (App-vNext#1530)

Fix DelayAsync extension (App-vNext#1525)