Resolved JERSEY-2540.

- Added config and request customizer SPI for Grizzly provider + unit test coverage.
- (Unrelated) Added utility CachingConnectorProvider implementation + unit test coverage.

Change-Id: Ie7c9f91a7cd5bd27b868fb433228b0cd77a1ecdf
Signed-off-by: Marek Potociar <marek.potociar@oracle.com>
Merge "Resolved JERSEY-2540."