feat: add createDefaultMetadataKeyInterceptor

[BlinkyStitt]

Why is this change needed?

Neynar requires x-api-key to access its hubs. This change makes it easy to include that (or any other) header.

I tried to follow the docs to create a changes, but got an error. Am I running it from the wrong directory maybe?

% yarn changeset
yarn run v1.22.22
error Command "changeset" not found.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
bryan@Bryan-Neynar hub-monorepo % yarn run changeset 
yarn run v1.22.22
error Command "changeset" not found.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Merge Checklist

Choose all relevant options below by adding an x now or at any time before submitting for review

• PR title adheres to the conventional commits standard
• PR has a changeset
• PR has been tagged with a change label(s) (i.e. documentation, feature, bugfix, or chore)
• PR includes documentation if necessary.

---

PR-Codex overview

This PR introduces a new function to create a metadata key interceptor for gRPC calls in the hub-nodejs package.

Detailed summary

• Added the createDefaultMetadataKeyInterceptor function in packages/hub-nodejs/src/client.ts.
• The function takes a key and value, returning an interceptor that sets the specified metadata key with the given value if it is not already present.

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}

[changeset-bot]

🦋 Changeset detected

Latest commit: 51790ca

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@farcaster/hub-nodejs	Patch

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Name	Status	Preview	Comments	Updated (UTC)
hub-monorepo	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 16, 2024 3:42am

[BlinkyStitt]

I don't see how that test failure could be caused by my change. This function isn't even used.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.

Project coverage is 44.16%. Comparing base (1880070) to head (51790ca).
Report is 401 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/hub-nodejs/src/client.ts	0.00%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2368       +/-   ##
===========================================
- Coverage   74.05%   44.16%   -29.90%     
===========================================
  Files          99      146       +47     
  Lines        9425    26203    +16778     
  Branches     2097     9272     +7175     
===========================================
+ Hits         6980    11572     +4592     
- Misses       2327    12815    +10488     
- Partials      118     1816     +1698     

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