Closes gh-6385

Closes gh-16581

* gh-16182:
  Polish "Determine Spring Boot version correctly when using module path"
  Determine Spring Boot version correctly when using module path

Closes gh-16182

See gh-16182

In Java 9, a package may return null for its implementation version
even when the manifest attribute specifying the version is present
in the jar from which the package was loaded.

This commit updates SpringBootVersion to fall back to
accessing the jar and its manifest attributes directly when the
implementation version of its package is null.

See gh-16182

* gh-16278:
  Polish "Add support for configuring remaining Undertow server options"
  Add support for configuring remaining Undertow server options

Closes gh-16278

See gh-16278

This commit adds support for configuring Undertow's server options that were previously
not configurable via application properties. The additions are the following:

- allow-encoded-slash
- always-set-keep-alive
- decode-url
- max-cookies
- max-headers
- max-parameters,
- url-charset

See gh-16278

* gh-16593:
  Update WebFlux starter to depend on validation starter

Closes gh-16593

Previously, the WebFlux starter declared direct dependencies on Hibernate Validator
and the Jakarta EE validation API. This meant that it required two exclusions to
exclude validation from a reactive web application that did not need it.

This commit updates the WebFlux starter to get its validation dependencies via a
dependency on the validation starter. This allows validation to be excluded
using a single exclusion. The EL dependency from the validation starter has
been excluded to allow the EL implementation from the underlying container
starter to continue to be used instead.

See gh-16593

* pr/15965:
  Polish "Allow to configure the Elasticsearch rest client timeouts"
  Allow to configure the Elasticsearch rest client timeouts

Closes gh-15965

See gh-15965

Closes gh-16600

Closes gh-16596

* pr/16467:
  Polish "Add auto-configuration support for ReactiveGridFsTemplate"
  Add auto-configuration support for ReactiveGridFsTemplate

Closes gh-16467

See gh-16467

* pr/16080:
  Polish "Complete Jetty Access Log configuration properties support"
  Complete Jetty Access Log configuration properties support

Closes gh-16080

See gh-16080

Closes gh-14989

Closes gh-14989

Closes gh-16591

Closes gh-16591

* pr/16575:
  Polish

Closes gh-16575

* pr/16575:
  Polish

See gh-16575

Closes gh-16499

Closes gh-16576

Closes gh-16499

Closes gh-5307

Closes gh-16579

Closes gh-16548