proxy http error classification

[conradludgate]

Problem

Missing error classification for SQL-over-HTTP queries.
Not respecting UserFacingError for SQL-over-HTTP queries.

Summary of changes

Adds error classification.
Adds user facing errors.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2508 tests run: 2383 passed, 0 failed, 125 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_ondemand_activation: debug

Code coverage* (full report)

• functions: 28.7% (7027 of 24492 functions)
• lines: 47.5% (43409 of 91463 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
008c0a7 at 2024-03-12T15:31:41.430Z :recycle:}