Update occurrence parameter description in regexp-replace

[OleksiiKovalov]

Clarified behavior of the occurrence parameter in regexp_replace.

[prmerger-automator[bot]]

@OleksiiKovalov : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod[bot]]

Learn Build status updates of commit 3eaca85:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
docs/t-sql/functions/regexp-replace-transact-sql.md	:white_check_mark:Succeeded

For more details, please refer to the build report.

[ktoliver]

@MikeRayMSFT

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged" @MicrosoftDocs/public-repo-pr-review-team

[MikeRayMSFT]

Reviewing.

[MikeRayMSFT]

@abhimantiwari - please review