Extract public sk types to safekeeper_api

[arssher]

Problem

We want to extract safekeeper http client to separate crate for use in storage controller and neon_local. However, many types used in the API are internal to safekeeper.

Summary of changes

Move them to safekeeper_api crate. No functional changes.

ref #9011

[github-actions]

7095 tests run: 6798 passed, 0 failed, 297 skipped (full report)

---

Flaky tests (1)

Postgres 17

• test_nbtree_pagesplit_cycleid: release-arm64

Code coverage* (full report)

• functions: 31.4% (8397 of 26778 functions)
• lines: 48.0% (66620 of 138650 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
7ee5d88 at 2024-12-13T13:59:53.121Z :recycle:}