Expose AwsCredentialsProvider to AmazonS3InstallationService

[bruceadowns]

I would like to extend AmazonS3InstallationService to provide a custom AwsCredentialsProvider.
This picks off where #1165 left off.
Same change will apply to AmazonS3OAuthStateService.

Proposed constructor:

    public AmazonS3InstallationService(String bucketName,
        AwsCredentialsProvider credentialsProvider,
        String region,
        String endpointUrl)

This accommodates a custom (i.e. spring) provider and allows for endpoint override to support DR scenarios and https:/localstack.cloud.

Category (place an x in each of the [ ])

• bolt (Bolt for Java)
• bolt-{sub modules} (Bolt for Java - optional modules)
• slack-api-client (Slack API Clients)
• slack-api-model (Slack API Data Models)
• slack-api-*-kotlin-extension (Kotlin Extensions for Slack API Clients)
• slack-app-backend (The primitive layer of Bolt for Java)

Requirements

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[seratch]

Thanks for the suggestion; your suggestion here makes sense. I've submitted a pull request adding a new contructor: #1419