Update launchdarkly-server-sdk to version 2.5.1

[teskje]

This updates the launchdarkly-server-sdk dependency to version 2.5.1.

We are still using our own fork mostly because it has MaterializeInc/rust-server-sdk@4d051dd which we can't easily upstream because it doesn't fully solve the issue (see Slack thread). We may be able to depend on upstream again once launchdarkly/rust-server-sdk#116 is resolved. We are able to move back to upstream for the rust-eventsource-client crate at least.

Motivation

• This PR updates a dependency.

Closes https://github.com/MaterializeInc/database-issues/issues/9113

Tips for reviewer

I rebased our rust-server-sdk fork by pushing to main directly, so there is no PR to review. However, you can view the changes relative to the upstream here. Also the old state of main is still available as the main-backup branch.

Checklist

• This PR has adequate test coverage / QA involvement has been duly considered. (trigger-ci for additional test/nightly runs)
• This PR has an associated up-to-date design doc, is a design doc (template), or is sufficiently small to not require a design.
• If this PR evolves an existing $T ⇔ Proto$T mapping (possibly in a backwards-incompatible way), then it is tagged with a T-proto label.
• If this PR will require changes to cloud orchestration or tests, there is a companion cloud PR to account for those changes that is tagged with the release-blocker label (example).
• If this PR includes major user-facing behavior changes, I have pinged the relevant PM to schedule a changelog post.

[antiguru]

Looks good, thank you!

[def-]

I have triggered nightly (https://buildkite.com/materialize/nightly/builds/11662) and asan (https://buildkite.com/materialize/nightly/builds/11663 & https://buildkite.com/materialize/test/builds/101430). I can check back on the results later today

[def-]

Test runs lgtm

[teskje]

TFTRs!