Release 0.54.0

[StephenWakely]

What does this PR do?

Prepares the 0.54.0 release: adds the CHANGELOG entry and bumps datadog/version.py.

Description of the Change

Follows RELEASING.md:

• CHANGELOG.md — new v0.54.0 section.
• datadog/version.py — 0.53.0 -> 0.54.0.

One PR has merged to master since v0.53.0:

• #979 — retry sending DogStatsD packets over UDS when the connection drops (changelog/Changed).

Minor bump rather than a patch because #979 is labelled changelog/Changed: it widens the meaning of the existing socket_connect_timeout option, which now also bounds send-retry rather than connect only. The behaviour is opt-in — socket_connect_timeout defaults to 0, which disables retries — so users who do not set it are unaffected.

Verification Process

• CHANGELOG.md entry follows the existing format and links to Retry the connection if a socket error is because the server went away. #979.
• python setup.py --version reports 0.54.0; from datadog.version import __version__ imports cleanly.
• No other file references the old version string.
• Note: ddev was not available locally, so the changelog entry was written by hand in the established format rather than generated via ddev release changelog.

Additional Notes

Not to be merged until reviewed. Per RELEASING.md, after this merges: create the GitHub release/tag, confirm the PyPI publish action, then open a follow-up PR bumping datadog/version.py to a dev version (e.g. 0.54.1.dev) — note that step appears to have been skipped after v0.53.0, since master was left at a flat 0.53.0.

Release Notes

• [Changed] Retry sending DogStatsD packets over UDS when the connection drops (opt-in via socket_connect_timeout). See #979.