`thar-be-registries`: `BTreeMap` key sorting breaks endpoint order in hosts.toml

[Riqardos]

Package I'm using:

thar-be-registries in bottlerocket-core-kit

What I expected to happen:

When configuring settings.container-registry.mirrors with multiple endpoints, the generated /etc/containerd/certs.d/<registry>/hosts.toml should preserve the endpoint order as specified. Since containerd uses section order as priority (first = primary, rest = fallback), endpoints should appear in hosts.toml in the same order they were configured.

What actually happened:

The endpoint order in hosts.toml does not match the configured order — endpoints are sorted alphabetically instead. This causes containerd to use an unintended endpoint as primary.

Verified on a live node:

• /etc/containerd/thar-be-registries.toml — endpoint order is correct (matches configuration)
• /etc/containerd/certs.d/docker.io/hosts.toml — endpoint order is wrong (sorted alphabetically)

# thar-be-registries.toml (CORRECT order)
[[mirrors]]
registry = "docker.io"
endpoint = [
  "https://mirror-a.example.com",
  "https://mirror-b.example.com"

# /etc/containerd/certs.d/docker.io/hosts.toml (WRONG order — sorted alphabetically)
server = "https://registry-1.docker.io"

[host."https://mirror-b.example.com"]
capabilities = ["pull", "resolve"]

[host."https://mirror-a.example.com"]
capabilities = ["pull", "resolve"]

How to reproduce the problem:

Configure two or more mirror endpoints whose URLs sort in a different alphabetical order than the intended priority order. Inspect the generated hosts.toml — endpoints will appear in alphabetical order regardless of the configured order.