feat: bootstrap with initial webhook receiver logic

[cbartz]

PR to add

• chore files like README, github workflows
• logic for webhook-gateway application (without redelivery action)

Follow-up PRs to add opentelemetry and 12F charm for the webhook-gateway application are planned

[cbartz]

Comments coming from review call

[Copilot]

Pull Request Overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull Request Overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated no new comments.

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[yanksyoon]

LGTM, thanks!