Add env var to disable rehydrate

[vicky-g]

Description

What is the purpose of this PR? What is the current behavior? New behavior? Relevant links (e.g. Trello) and/or information pertaining to PR?

Disable rehydrate depending on env var value disableRehydrate

Tests

List the manual tests and repro instructions to verify that this PR works as anticipated. Include log analysis if possible.
❗ If this change impacts clients, make sure that you have tested the clients ❗

1. Added log statement to check if variable works as intended (only for testing):

  async addRehydrateIpfsFromFsIfNecessaryTask (multihash, storagePath, { logContext }, filename = null) {
    if (enableRehydrate) {
      console.log('I AM ADDING A REHYTDRATE TASKKSK')
      this.logStatus(logContext, 'Adding a rehydrateIpfsFromFsIfNecessary task to the queue!')
      const count = await this.queue.count()
      if (count > MAX_COUNT) return
      const job = await this.queue.add(
        PROCESS_NAMES.rehydrate_file,
        { multihash, storagePath, filename, logContext }
      )
      this.logStatus(logContext, 'Successfully added a rehydrateIpfsFromFsIfNecessary task!')

      return job
    }
  }

2. Hit the /ipfs/:CID route with an existing CID
3. Checked CN logs

Zc-aaA, requestMethod=GET, requestHostname=localhost)
    requestUrl: /ipfs/QmcUQgQWkUtwtEZWupG6HK1gyhhhN5eNeDa6pFBBaMnXWk
I AM ADDING A REHYTDRATE TASKKSK
[2021-04-02T00:16:23.672Z]  INFO: audius_creator_node/7223 on af34b1ef01a9: Retrieving /file_storage/files/nXW/QmcUQgQWkUtwtEZWupG6HK1gyhhhN5eNeDa6pFBBaMnXWk directly from filesystem (requestID=7fIZc-aaA, requestMethod=GET, requestHostname=localhost)
    requestUrl: /ipfs/QmcUQgQWkUtwtEZWupG6HK1gyhhhN5eNeDa6pFBBaMnXWk

4. Made sure that I was still able to retrieve the contents of the CID (metadata showed up in URL)

[dmanjunath]

Fixed https://linear.app/audius/issue/AUD-483/env-var-to-turn-rehydrate-off-in-content-node