Configuration additions

[MDerman]

Add shared host configuration conventions

Summary

Adds Odin.Configuration.Hosting, giving Soulv hosts one standard way to load configuration: app settings, host-specific extras, user secrets, environment variables, then Azure Key Vault last.

Why

Hosts need consistent startup config and Key Vault behavior. Centralizing this reduces duplicate setup and makes local/dev vs deployed credential behavior explicit.

What changed

• Added AddHostConfiguration(...) and AddKeyVaultConfiguration(...).
• Added options for appSettings location, extra sources, user secrets, env vars, Key Vault section, local environments, and default secret prefix derivation.
• Supports Key Vault auth via configured client secret, env client secret, or user-assigned managed identity.
• Tightened prefixed Key Vault helper: required/trimmed prefix, ordinal prefix matching, HTTPS-only vault URIs, no path/query in vault URI.
• Added tests covering source precedence, Key Vault skip/error paths, credential selection, prefix derivation, URI validation, and prefix matching.

Main files

• HostConfigurationExtensions.cs
• HostConfigurationOptions.cs
• KeyVaultConfigurationOptions.cs
• ConfigurationBuilderExtensions.cs
• PrefixedAzureKeyVaultSecretManager.cs
• HostConfigurationExtensionsTests.cs
• PrefixedAzureKeyVaultSecretManagerTests.cs