fix: Skip frontend Sentry init if DSN is not set

[roikarinen61n]

• Skip frontend Sentry init if DSN is not set
• Add documentation on how to disable Sentry
• Related to Offline access for tagging sensitive data #4612

PR fulfills these requirements

• Commit message(s) and PR title follows the format [fix|feat|ci|chore|doc]: TICKET-ID: Short description of change made ex. fix: DEV-XXXX: Removed inconsistent code usage causing intermittent errors
• Tests for the changes have been added/updated (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)
• Best efforts were made to ensure docs/code are concise and coherent (checked for spelling/grammatical errors, commented out code, debug logs etc.)
• Self-reviewed and ran all changes on a local instance (for bug fixes/features)

Change has impacts in these area(s)

(check all that apply)

• Product design
• Backend (Database)
• Backend (API)
• Frontend

Describe the reason for change

• Related to Offline access for tagging sensitive data #4612
• Sentry initialization is made and monitoring messages sent to sentry even when FRONTEND_SENTRY_DSN environment variable is set to empty string.

What does this fix?

• The sentry monitoring gets now disabled correctly in frontend

What is the new behavior?

N/A

What is the current behavior?

N/A

What libraries were added/updated?

N/A

Does this change affect performance?

No

Does this change affect security?

N/A

What alternative approaches were there?

N/A

What feature flags were used to cover this change?

N/A

Does this PR introduce a breaking change?

(check only one)

• Yes, and covered entirely by feature flag(s)
• Yes, and covered partially by feature flag(s)
• No
• Not sure (briefly explain the situation below)

What level of testing was included in the change?

(check all that apply)

• e2e
• integration
• unit

Which logical domain(s) does this change affect?

Monitoring

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