Reverts #8425

#### Reference Issues/PRs
Closes #8434 

#### What does this implement/fix? Explain your changes.
Re-add some extensions to conf.py

@mateuszkasprowicz's excellent PR
#8385 fixed the doc build, though
as a side effect of simplifying it also removed a few extensions:

* extension required for links in changelogs, `sphinx_issues`
* extension required for panels and buttons in overviews,
`sphinx_design`

These are added back in this PR.

Fixes some linting issues on the `docs/conf.py`

increase `joblib` bound to `joblib<1.7`, to be released with 0.38.0

Reverts the documentation build PR #8385 until the issues are resolved.

The newly erleased `scipy 1.16` has removed some private utilities which
were imported by a number of time series packages.

This PR adds a bound `scipy<1.16` to those estimators, and a todo check
for release managers to check compatibility at next minor release.

Raises the `numpy` bound to allow `numpy<2.4`.

Depends on #8447 for testing.

Carries out deprecations and change actions scheduled for 0.37.0:

* remove deprecated methods from `BaseBenchmark` and
`forecasting_validation`
* updated `prophetverse` delegator bounds
* remove `proba` module which has moved to `skpro`
* bump deprecation/change checks scheduled for 0.38.0 to 0.39.0 or 1.0.0

TSC data loaders in `sktime` uses datasets in `.ts` format, but some of
the datasets that come pre-loaded with `sktime` contains same datasets
in 2-3 format. This is likely due to their original host
[https://www.timeseriesclassification.com](https://www.timeseriesclassification.com)
which contains `zip` of datasets in different formats.

This PR removes the redundant dataset files and reduces the repository
size by around 7.5 MB which is significant.

… to >=1.1,<2.4.0 (#8349)

Updates the requirements on
[pandas](https://github.com/pandas-dev/pandas) to permit the latest
version.

`sklearn 1.7` compatibility patch:

* version dependent handling of `sklearn` tag system
* version dependent handling of `sklearn` `validate_data` mechanism

Reconcilers were not available in API reference

Raises the `scikit-learn` bound to `<1.8.0` to allow the recently
released `scikit-learn 1.7.0`.

Depends on #8439 for testing.

Release PR for 0.38.0

* version number bump
* changelog

instant release action for 0.38.0