fix: separate server connection config

[markpmarton]

Description

The PR separates server-side connection requirements from client connection policy by introducing ServerConnectionConfig as a dedicated type, distinct from ClientConfig.

Previously, the full ClientConfig (including client-local settings like Spire socket paths, backoff, keepalive) was serialized and stored in the database and passed over the wire. Now the control plane stores and transmits only what the server requires — endpoint, TLS flag, and auth method — while the controller merges those requirements onto its own local ClientConfig when opening a connection.

Changes

• Dedicated ServerConnectionConfig type containing only remote connection related fields
• In ConnectionDetails db schema SpireMtls nested field is replaced with three flat fields (tls_required, auth_method and spire_trust_domain)
• generate_config_data simplified: unused src_node removed
• tls_required == true is now mandatory if auth_method is Spire

Type of Change

• Bugfix
• New Feature
• Breaking Change
• Refactor
• Documentation
• Other (please describe)

Checklist

• I have read the contributing guidelines
• Existing issues have been referenced (where applicable)
• I have verified this change is not present in other open pull requests
• Functionality is documented
• All code style checks pass
• New code contribution is covered by automated tests
• All new and existing tests pass