Docs: Update broken url in supported secrets section in the Secret Detection page

What does this MR do?

This is a small fix for a URL in the secret detection page, specifically the Supported Secrets section, whereby the statement "The default ruleset provided by Gitleaks includes the following key types" has a link to the gitleaks.toml file but the current link points to a gitleaks directory, then the gitleaks.toml file but the file itself is in the root of the repository.

One ends up getting a "gitleaks/gitleaks.toml" did not exist on "master" message. This was communicated by a customer (via a Zendesk Ticket) but when submitting the MR, in their words, the pages loads forever and after ~60sec they get a 500 error page.

Hopefully this works for me.

Related issues

ActiveRecord::InvalidForeignKey: PG::ForeignKeyViolation: ERROR: insert or update on table "merge_request_metrics" violates forei...

Author's checklist

• Follow the Documentation Guidelines and Style Guide.
• Ensure that the product tier badge is added to doc's h1.
• Request a review based on the documentation page's metadata and associated Technical Writer.

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Review checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
• Ensure a release milestone is set.