Always auto-generate the agent id and remove the AgentId / instance_suffix configuration

Summary

The agent id is currently a user-configurable setting (AgentId YAML key, PINPOINT_CPP_AGENT_ID environment variable), with extra machinery to keep pinned ids unique across pre-fork workers (AgentOptions::instance_suffix / pt_agent_options_set_instance_suffix(), pid-suffix fallback). This complicates identity resolution, while the collector only requires the id to be unique per agent instance — a display label is what users actually want to control.

Proposed changes

1. Remove the agent id configuration; always auto-generate

• Drop the AgentId YAML key and the PINPOINT_CPP_AGENT_ID environment variable.
• Always auto-generate the agent id at startup as a 22-char URL-safe Base64 UUIDv7 (uniform across UidVersion v1/v3/v4), so every process — including sibling pre-fork workers — gets a unique id by construction.
• A config reload keeps the running agent id (identity is non-reloadable).
• AgentName remains the human-readable label and falls back to the generated id when omitted.

2. Remove the instance_suffix feature

With the id always auto-generated per process, the per-worker suffix machinery has no remaining purpose:

• Remove AgentOptions::instance_suffix and the C API pt_agent_options_set_instance_suffix().
• Use a configured AgentName verbatim — it need not be unique across workers.
• Remove the %suffix% placeholder in Log.FilePath (%pid% remains for per-worker log files).

3. Fix a spurious reload warning for UidVersion: v4

resolve_v4() regenerates a fresh UUIDv7 on every make_config() call, so every v4 config-file reload carried a new agent_id_, tripping isReloadable() inside retainNonReloadableFrom() and logging a spurious "non-reloadable config fields changed at runtime" warning even when the file did not change. Re-resolution on reload should keep the running agent id (and its UUID) intact.

Start by tracing config resolution through resolve_v4(), make_config(), and retainNonReloadableFrom(), then inspect AgentOptions and the pt_agent_options_set_instance_suffix() API. Check the AgentId, PINPOINT_CPP_AGENT_ID, AgentName, and Log.FilePath handling described in the issue. Done means per-process generated ids remain stable across reloads, instance_suffix and %suffix% are removed, and the obsolete reload warning no longer appears.