Update changelog for 0.18.0 release

[antonwolfy]

The PR adds missing entries to the changelog and sets the release date.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html

[github-actions]

Array API standard conformance tests for dpnp=0.19.0dev0=py312h509198e_7 ran successfully.
Passed: 1231
Failed: 0
Skipped: 9

[coveralls]

coverage: 71.763%. remained the same
when pulling 07f07ec on correct-changelog-for-0.18.0
into ccc36a2 on master.