Fix for cdf announcement metrics

[coot]

Description

CDFs needs to be populated once we are in sync (e.g. when announcment
delay is less than 20s old).

I confirmed the CDFs are available via prometheus:

$ curl 127.0.0.1:12798/metrics 2&>/dev/null | rg cardano | rg cdf
cardano_node_metrics_leios_eb_announcement_delay_cdf1400ms_real 0.875
cardano_node_metrics_leios_eb_announcement_delay_cdf2000ms_real 0.9
cardano_node_metrics_leios_eb_announcement_delay_cdf1200ms_real 0.8583333333333333
cardano_node_metrics_leios_eb_announcement_delay_cdf800ms_real 0.6416666666666667
cardano_node_metrics_leios_eb_announcement_delay_cdf1000ms_real 0.6916666666666667
cardano_node_metrics_leios_eb_announcement_delay_cdf200ms_real 7.5e-2
cardano_node_metrics_leios_eb_announcement_delay_cdf1800ms_real 0.8916666666666667
cardano_node_metrics_leios_eb_announcement_delay_cdf600ms_real 0.55
cardano_node_metrics_leios_eb_announcement_delay_cdf1600ms_real 0.8833333333333333
cardano_node_metrics_leios_eb_announcement_delay_cdf400ms_real 0.375

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • roundtrip tests
  • integration tests
    See Running tests for more details
• Any changes are noted in the CHANGELOG.md for affected package
  • cardano-node-chairman, cardano-submit-api and cardano-testnet instead need a
    changelog fragment in <package>/.changes/, because their CHANGELOG.md is generated
    from fragments at release time. Copy _TEMPLATE.yml from that directory, or run
    nix run github:input-output-hk/cardano-dev#herald -- new
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
  • Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • Code builds on Linux, MacOS and Windows for ghc-9.6 and ghc-9.12
• Self-reviewed the diff

Note on CI

If your PR is from a fork, the necessary CI jobs won't trigger automatically for security reasons.
You will need to get someone with write privileges. Please contact IOG node developers to do this
for you.

[nfrisby]

👍