Return undefined from getOrderbookMidPriceMap (backport #2441)

[mergify]

Changelist

Removes code that hits the OrderbookCache when generating candles. This change will be fixed in a later update

Summary by CodeRabbit

• Bug Fixes

  • Streamlined test cases by removing redundant checks related to order book mid prices.
  • Adjusted expectations in tests to reflect changes in handling order book prices.

• New Features

  • Updated the getOrderbookMidPriceMap function to return undefined for order book mid prices, indicating a shift in data retrieval logic.

• Refactor

  • Removed Redis integration for fetching median prices, simplifying the price retrieval process in the CandlesGenerator.

---

This is an automatic backport of pull request #2441 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 9fecfc5 has failed:

On branch mergify/bp/release/indexer/v7.x/pr-2441
Your branch is up to date with 'origin/release/indexer/v7.x'.

You are currently cherry-picking commit 9fecfc5d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   indexer/services/ender/src/lib/candles-generator.ts

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   indexer/services/ender/__tests__/lib/candles-generator.test.ts

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