fix: replace user identity strings with user IDs (#38775)

[vgulati-apphelix]

Update application logging to prevent exposure of customer identity information in logs when SQUELCH_PII_IN_LOGS is enabled. Log records that currently include usernames, email addresses, or other user-identifying strings should instead use non-PII identifiers (for example, numeric user IDs) where appropriate.

Description

Describe what this pull request changes, and why. Include implications for people using this change.
Design decisions and their rationales should be documented in the repo (docstring / ADR), per
OEP-19, and can be
linked here.

Useful information to include:

• Which edX user roles will this change impact? Common user roles are "Learner", "Course Author",
  "Developer", and "Operator".
• Include screenshots for changes to the UI (ideally, both "before" and "after" screenshots, if applicable).
• Provide links to the description of corresponding configuration changes. Remember to correctly annotate these
  changes.

Supporting information

Link to other information about the change, such as Jira issues, GitHub issues, or Discourse discussions.
Be sure to check they are publicly readable, or if not, repeat the information here.

Testing instructions

Please provide detailed step-by-step instructions for testing this change.

Deadline

"None" if there's no rush, or provide a specific date or event (and reason) if there is one.

Other information

Include anything else that will help reviewers and consumers understand the change.

• Does this change depend on other changes elsewhere?
• Any special concerns or limitations? For example: deprecations, migrations, security, or accessibility.
• If your database migration can't be rolled back easily.