Validate client IDs before applying them

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

Description

OpenId Connect Client IDs should only be made up of "unreserved characters" - that is, [a-z], [A-Z], [0-9] and [-._~] (see https://en.wikipedia.org/wiki/Percent-encoding).

The back-office client already limits the Client ID input to alphanumerical chars and dash, but of course the API also needs a validation - and that's what this PR adds 😄

Testing this PR

You'll need to use Swagger to test this, due to the above-mentioned restrictions in the back-office.

1. It should be possible to create Client IDs for API Users which consists of valid chars.
2. It should not be possible to create Client IDs for API Users containing one or more invalid chars.

[Zeegaan]

Took the liberty of adding a reponse for the operation result 😁
Looks good, tests good 🚀

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 suggestion.

Files not reviewed (1)

• src/Umbraco.Infrastructure/Security/BackOfficeUserClientCredentialsManager.cs: Evaluated as low risk