feature: making Slack action URL configurable

[jkeyes]

Problem

The "Open view" action in the Slack alert it refers to http://localhost instead of the server where it is deployed.

Solution

Add a Host field to the [slack] section of config.toml. If this field is non-empty use it as the base for the "Open view" Action URL, otherwise default to http://localhost:{port}.

Changes Made

• added Host field to the SlackConfig struct
• refactored the slack.Attachment creation code into its own function
• added a host parameter to the hitSlackWebhook function
• updated docs to include the new field
• added webhook_test.go to test the new createSlackAttachment function
• added config_test.go to test the new Host field

How to Test

• set host in config.toml to https://example.com
• create an alert that can easily be triggered e.g. resource count > 0
• click the "Open view" action in the Slack alert
• verify the browser attempts to open https://example.com/inventory?view={viewId}

Screenshots

None.

Notes

None.

Checklist

• Code follows the contributing guidelines
• Changes have been thoroughly tested
• Documentation has been updated, if necessary
• Any dependencies have been added to the project, if necessary

Reviewers

@[username of the reviewer]

[github-actions]

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[Azanul]

Really liked what you did with createSlackAttachment