feat(router): add configurable connection limits for each subgraph

[endigma]

• feat(router): add configurable connection limits for each subgraph
• test: update snapshots

Motivation and Context

Users want to configure connection limits for the router, including per-subgraph values.

Checklist

• I have discussed my proposed changes in an issue and have received approval to proceed.
• I have followed the coding standards of the project.
• Tests or benchmarks have been added or updated.
• Documentation has been updated on https://github.com/wundergraph/cosmo-docs.
• I have read the Contributors Guide.

Example config utilizing this feature:

traffic_shaping:
  all:
    max_idle_conns: 1024
    max_conns_per_host: 100
    max_idle_conns_per_host: 20
  subgraphs:
    employees:
      max_idle_conns: 4096
      max_conns_per_host: 400
      max_idle_conns_per_host: 80

[github-actions]

Router image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-b621693eac889c651674a00960a9b0bbf2412baf

[endigma]

With the changes introduced in #1567 this PR is now a good bit simpler and the previously somewhat complex interaction with TimeoutTransport is now gone.

[StarpTech]

LGTM