CONFIG: Upgrade ADotNet to 6.0.0 and update NuGet packages

[morgang-adappt]

Summary

This PR does the following for NHSDigital.ApiPlatform:

• ADotNet 6.0.0: the build workflow tags with the workflow GITHUB_TOKEN and publishes with NuGet Trusted Publishing, so it no longer uses PAT_FOR_TAGGING or NUGET_ACCESS.
• Package updates: every package not held back for another reason moves to the latest stable version.

It supersedes Dependabot #35, #36, #37, #38 and #39.

closes #44

Dependency updates (CONFIG)

• coverlet.collector: 10.0.1 -> 10.1.0
• Hl7.Fhir.STU3: 6.4.0 -> 6.6.0
• Microsoft.Extensions.Configuration, Microsoft.Extensions.Configuration.Binder, Microsoft.Extensions.Configuration.EnvironmentVariables, Microsoft.Extensions.Configuration.Json, Microsoft.Extensions.DependencyInjection, Microsoft.Extensions.Http, Microsoft.Extensions.Logging: 10.0.10 -> 10.0.12
• Moq: 4.20.72 -> 4.21.0
• WireMock.Net: 2.13.0 -> 2.19.0
• ADotNet: 5.1.0 -> 6.0.0

Not changed:

• FluentAssertions stays pinned at [7.2.2].
• The xunit packages and Microsoft.NET.Test.Sdk are left for the xunit 4 / Microsoft Testing Platform move.

Workflow regeneration (CODE RUB)

• add_tag now uses TagJobV3. Checkout and the GitHub release use GITHUB_TOKEN, and the job has permissions: contents: write.
• publish now uses NugetTrustedPublishingJob. A NuGet/login@v1 step exchanges the job's GitHub OIDC token for a NuGet API key that lasts one hour. The job has permissions: id-token: write and contents: read.
• build.yml was regenerated from NHSDigital.ApiPlatform.Infrastructure, not hand-edited.
• prLinter.yml was regenerated as well. It had not been regenerated since an older ADotNet, so it picks up the expanded MINOR/MEDIUM/MAJOR label prefixes and the try/catch around assigning the PR author that the other repositories already have.

Before the next release

This is the same setup LondonDataServices.OlidsToFhirMapper used to release 0.2.0.2:

• nuget.org: add a Trusted Publishing policy with owner NHSISL, repository NHSDigital.ApiPlatform, workflow build.yml, and an empty environment.
• GitHub: make sure this repository can use the NHSISL organisation secret NUGET_USER.

Without these, the next release still creates the tag and the GitHub release, but the NuGet publish step fails.

Validation (local)

• Build: 0 errors. The 68 CS8632 warnings are the same as on main.
• Vulnerabilities: dotnet list package --vulnerable --include-transitive reports none.
• Tests: Sdk Unit (221), Sdk Acceptance (24), Sdk.AspNetCore Unit (19) and Sdk.AspNetCore Acceptance (10) pass.