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This PR enforces that the tenant create / update-config APIs reject requests with unknown fields. This is a desirable property because some tenant config settings control the lifetime of user data (e.g., GC horizon or PITR interval). Suppose we inadvertently rename the `pitr_interval` field in the Rust code. Then, right now, a client that still uses the old name will send a tenant config request to configure a new PITR interval. Before this PR, we would accept such a request, ignore the old name field, and use the pageserver.toml default value for what the new PITR interval is. With this PR, we will instead reject such a request. One might argue that the client could simply check whether the config it sent has been applied, using the `/v1/tenant/.../config` endpoint. That is correct for tenant create and update-config. But, attach will soon [^1] grow the ability to have attach-time config as well. If we ignore unknown fields and fall back to global defaults in that case, we risk data loss. Example: 1. Default PITR in pageservers is 7 days. 2. Create a tenant and set its PITR to 30 days. 3. For 30 days, fill the tenant continuously with data. 4. Detach the tenant. 5. Attach tenant. Attach must use the 30-day PITR setting in this scenario. If it were to fall back to the 7-day default value, we would lose 23 days of PITR capability for the tenant. So, the PR that adds attach-time tenant config will build on the (clunky) infrastructure added in this PR [^1]: https://github.com/neondatabase/neon/pull/4255 Implementation Notes ==================== This could have been a simple `#[serde(deny_unknown_fields)]` but sadly, that is documented- but silent-at-compile-time-incompatible with `#[serde(flatten)]`. But we are still using this by adding on outer struct and use unit tests to ensure it is correct. `neon_local tenant config` now uses the `.remove()` pattern + bail if there are leftover config args. That's in line with what `neon_local tenant create` does. We should dedupe that logic in a future PR. --------- Signed-off-by: Alex Chi <iskyzh@gmail.com> Co-authored-by: Alex Chi <iskyzh@gmail.com>