[6.3] Use CC_ENABLE_WORKER_HEALTH_MONITOR knob to guard remoteDCIsHealthy logic

[halfprice]

Cherry pick #6105

Code-Reviewer Section

The general guidelines can be found here.

Please check each of the following things and check all boxes before accepting a PR.

• The PR has a description, explaining both the problem and the solution.
• The description mentions which forms of testing were done and the testing seems reasonable.
• Every function/class/actor that was touched is reasonably well documented.

For Release-Branches

If this PR is made against a release-branch, please also check the following:

• This change/bugfix is a cherry-pick from the next younger branch (younger release-branch or master if this is the youngest branch)
• There is a good reason why this PR needs to go into a release branch and this reason is documented (either in the description above or in a linked GitHub issue)

[foundationdb-ci]

AWS CodeBuild CI Report for Linux CentOS 7

• CodeBuild project: foundationdb-pr
• Commit ID: 4a8c511
• Result: SUCCEEDED
• Error: N/A
• Build Logs (available for 30 days)

[RenxuanW]

The commit history doesn't look correct.

[xumengpanda]

LGTM after change the PR against 6.3 instead of master.

[halfprice]

LGTM after change the PR against 6.3 instead of master.

Thank you!