Improve ingestion server slack alerts

[AetherUnbound]

Description

This PR changes the formatting of exception message slack alerts so that the entire exception body appears in preformatted text. It also adds an alert at the start of one-off reindex tasks.

Testing Instructions

1. Perform a reindex locally
2. Check that the message function has called (it will produce a DEBUG log to show it has been called).

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

Developer Certificate of Origin

Developer Certificate of Origin

Developer Certificate of Origin
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Developer's Certificate of Origin 1.1

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    have the right to submit it under the open source license
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    of my knowledge, is covered under an appropriate open source
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