Add parameter of key file path for AWS KMS plugin

AWS KMS plugin saves all key files under the root folder of data
directory. Increasing of the key IDs and key rotations will generate a
lot of key files under the root folder, looks messy and hard to
maintain the folder permission etc.

Now introduce a new plugin parameter `aws_key_management_keyfile_dir` to
define the directory for saving the key files for better maintenance.

Detailed parameter information as following:
```
        VARIABLE_NAME: AWS_KEY_MANAGEMENT_KEYFILE_DIR
        SESSION_VALUE: NULL
         GLOBAL_VALUE: <Directory path>
  GLOBAL_VALUE_ORIGIN: COMMAND-LINE
        DEFAULT_VALUE:
       VARIABLE_SCOPE: GLOBAL
        VARIABLE_TYPE: VARCHAR
     VARIABLE_COMMENT: Define the directory in which to save key files
                       for the AWS key management plugin. If not set,
                       the root datadir will be used
            READ_ONLY: YES
COMMAND_LINE_ARGUMENT: REQUIRED
    GLOBAL_VALUE_PATH: NULL
```

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.

0 files changed, 0 insertions, 0 deletions