Add bitbucket example for secrets

[kprosise]

Added as tabbed content, which is largely the same.

QA: Edited with linter on, and checked built content in browser.

This commit applies to issue FFTK-3400, "…Bitbucket git secrets config…"

PR Template and Checklist

Please complete as much as possible to speed up the reviewing process.
You may delete items that are not relevant to your contribution.
Readiness and adding reviewers as appropriate is required.

All PRs should be reviewed by a technical writer/documentation team and a peer.
If effecting customers—which is a majority of content changes—a member of Customer Success must also review.

Readiness

• Merge (pending reviews)
• Merge after date or event
• Draft

Checklist

• Run spelling and grammar check, preferably with linter.
• Review for wordiness
• Match tone and style of page/section.
• Run make linkcheck, and add redirects for any moved or deleted pages.
• View HTML in a browser to check rendering.
• Use semantic newlines.
• follow best practices for commits.
  • Descriptive title written in the imperative.
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  • Sign commit with your gpg key (-S, --gpg-sign).
  • Squash commits if needed.
• Request PR review by a technical writer and at least one peer.

Comments

Was not sure if we wanted to expand on the info on the submodule page as well. Kept it to a single page, copying what was linked to in the related Jira issue.

[vanmaegima]

LGTM, this looks neat!