Add secret masking for the telemetry.publish command

[DenisNikulin5]

In this PR, I added the use of the SecretMasker for telemetry.publish command to prevent leaking tokens (including JWT).

By default, the SecretMasker hasn't used cred scan patterns, they could be enabled only using the environment variable.
To use them via a feature flag, I have to move the logic of using the knob from the HostContext to the ExecutionContext and added a runtime source for this knob as well.

P.S. This change must be under the feature flag definitely since I found a comment where it was written that the cred scan could affect the agent performance. But I couldn't confirm this after testing the changes.

Testing:
To test the changes I used the DevFabric environment (Microsoft DevBox).
Testing steps:

1. Build and deploy DevFabric from the branch with the DistributedTask.Agent.MaskUsingCredScanRegexe feature flag.
2. Build and connect the agent to the test organization from the PR branch.
3. Add the test pipeline from this description and run it. It contains explicit telemetry.publish command with an exposed JWT token.
4. Check the results in the VSODev database, the CustomerIntelligence table. The result could be filtered by the name of the Feature. It will contain the RAW JWT since the feature flag is turned off.
5. Set the feature flag using LightRail tfs. Navigate to /tfs/DevFabric and run "Set-FeatureFlag -featureName DistributedTask.Agent.MaskUsingCredScanRegex -State ON".
6. Repeat 3-4 steps. The results will contain the masked JWT token.

• Test pipeline:

trigger:
- master

pool: Default

steps:
- powershell: |
    Write-Host "##vso[telemetry.publish area=AzurePipelinesAgent;feature=denikulin_Test]{"jwt" : "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWUsImlhdCI6MTY5NTg4OTY3NCwiZXhwIjoxNjk1ODkzMjc0fQ.hdiPa_gTPATGWr6-5gF25QEMAWmHU2MXZ4ED6-w0HW8"}"
  displayName: 'Run script'

Results:

• Before the change:
  
• After the change: