Since the move to JUnit 5, a number of tests were failing on Windows.
The majority were failing due to open file handles preventing the
clean up of the tests' temporary directory. This commit addresses
these failures by updating the tests to close JarFiles, InputStreams,
OutputStreams etc.

A change has also been made to CachingOperationInvokerTests to make
a flakey test more robust. Due to System.currentTimeMillis() being
less precise on Windows than it is on *nix platforms, the test could
fail as it would not sleep for long enough for the TTL period to have
expired.

Closes gh-17126

* pr/17129:
  Polish "Use existing properties field"
  Use existing properties field

Closes gh-17129

See gh-17129

See gh-17129

Fix polish commit from 919913ae to correctly name the property
getter/setters.

See gh-17022

See gh-17096

* pr/17022:
  Polish "Add session property for ConfigureRedisAction"
  Add session property for ConfigureRedisAction

Closes gh-17022

See gh-17022

Add a new property to `RedisSessionProperties` that allows the default
`ConfigureRedisAction` to be changed. Users can still also configure
the action using a `@Bean`.

See gh-17022

* pr/17091:
  Polish "Support default headers with RestTemplateBuilder"
  Support default headers with RestTemplateBuilder

Closes gh-17091

Broaden the scope of customizer support so that instead of focusing
just on headers, we can now customize any outgoing `HttpClientRequest`.
Also update auto-configuration to automatically add any
`RestTemplateRequestCustomizer` beans to the builder.

See gh-17091

Update `RestTemplateBuilder` so that it is easier to apply custom
headers to the outgoing request. The update is particularly useful
for setting the `User-Agent` header, for example so that a GitHub
username can be used when calling `api.github.com`.

See gh-17091

Closes gh-17086

This commit changes the default file extension for Freemarker templates
from `*.ftl` to `*.ftlh`. This commit also enables by default the
Freemarker setting `"recognize_standard_file_extensions"` to ensure that
HTML escaping is performed by default in Spring Boot applications.

Applications should adapt to this change by changing the file extensions
of existing templates to `.ftlh`.

Closes gh-15131

Closes gh-17127

Closes gh-17124

Fixes gh-17123

Closes gh-17122

Fixes gh-17121

Closes gh-17120

Closes gh-17119

Closes gh-17118

Fixes gh-17115

Closes gh-17114

Fixes gh-17095

Closes gh-17112

* gh-17111:
  Make dependency available for javadoc generation

Closes gh-17111

See gh-17111

Closes gh-17109

* pr/17069:
  Add missing @Test annotations

Closes gh-17069

This commit also restores assertion accidentally removed in
commit 44d83215.

See gh-17069

* pr/17106:
  Fix deployment tests JUnit 5 checkstyle issues

Closes gh-17106

See gh-17106

Closes gh-17104

Closes gh-17099