Change link for QFT documentation in the template page

[rmoyard]

Context:

Wrong link in the template documentation page.

Description of the Change:

pennylane.templates.subroutines.QuantumFourierTransform.html replaced by pennylane.templates.subroutines.QFT.html

Related GitHub Issues:

Closes #1728

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

Merging #1730 (28eef56) into master (949f5d5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1730   +/-   ##
=======================================
  Coverage   99.21%   99.21%           
=======================================
  Files         204      204           
  Lines       15425    15425           
=======================================
  Hits        15304    15304           
  Misses        121      121           

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[antalszava]

Thank you 🙏