[chatbot] Support setting log retention and expose metric methods in SlackChannelConfiguration

[humanzz]

With the recent changes to LogRetention construct in #9671 and #9703 and the creation of SlackChannelConfiguration construct in #9679, this is a follow up to request that SlackChannelConfiguration exposes log retention property and metric utility methods (similar to Lambda function)

Use Case

1. Set log retention on the slack channel configuration log that lives in a different region
2. Access slack channel configuration metrics easily

Proposed Solution

Inspired by the implementation in Lambda function

1. Add props for log retention
2. Add metric and metricAll methods

Other

Associate #8636

SlackChannelConfiguration is different from Lambda in that it is a global service writing cloudwatch logs/metrics to us-east-1 regardless of the region of the stack they live in.

I wanted to expose a logGroup() method similar to lambda but the current implementation for importing the log group from arn returns an ILogGroup which implements methods e.g. addStream, addMetricFilter which I think assume the log is in the same region so might introduce bugs.

I'm interested to hear your thoughts on this.

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

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This is a 🚀 Feature Request