Version 0.7.3

[mxmCherry]

All the changes since v0.7.2 are just dep bumps

[mxmCherry]

This is first release since v0.7.2 (from past year). Few dep bumps were done since that, but they were never released.

I eyeballed commits/PRs since prev version - doesn't seem to include any serious (major) version bumps.

Let's keep it this way - low-effort maintenance, just critical updates for now.

I also don't see any Github CI workflow to release the gem, though it's present on rubygems: https://rubygems.org/gems/datadog-notifications

@dim to merge, tag and release to rubygems.