Add Async proxy configuration support for AWS Kinesis/Cloudwatch input

[Nithin-Kasam]

Description

Added async proxy configuration support for AWS Kinesis/CloudWatch input by introducing a new AWSAsyncProxyConfigurationProvider class.

Motivation and Context

The existing AWSProxyConfigurationProvider uses the Apache HTTP client, which cannot be used by AWS async clients (DynamoDB, CloudWatch, Kinesis) that the Kinesis input relies on. The Kinesis Client Library additionally requires HTTP/2, which is only supported by the Netty async client. This change enables the Kinesis/CloudWatch input to work through the configured Graylog HTTP proxy.

closes https://github.com/Graylog2/graylog-plugin-enterprise/issues/14460

How Has This Been Tested?

-> Installed tiny proxy in my system.
-> Configured tiny.cfg file with
port 8888
Listen 0.0.0.0
Allow 127.0.0.1
ConnectPort 443
ConnectPort 80
-> Run the file . tinyproxy -c tiny.cfg
-> Configured http_proxy_uri = http://graylog:password12345@127.0.0.1:8888 in graylog.conf file
-> Verified logs by creating the input.

Added comprehensive unit tests in [AWSAsyncProxyConfigurationProviderTest.java] covering:

• Proxy configuration without credentials
• Proxy configuration with username/password credentials
• Proxy configuration with username only (no password)
• HTTPS proxy with credentials
• Default HTTP port fallback (80)
• Default HTTPS port fallback (443)

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have requested a documentation update.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.