Templates end with .tmpl

[mboersma]

What this PR does / why we need it:

Changes the filename extension of template files from .t to .tmpl, which seems more standard in the Go ecosystem. Also cues GitHub's language detection to consider these files as Go (currently they are misdetected as Perl 6).

Special notes for your reviewer:

If applicable:

• documentation
• unit tests
• tested backward compatibility (ie. deploy with previous version, upgrade with this branch)

Release note:

Change the filename extension of template files from `.t` to `.tmpl`

[tariq1890]

/lgtm

[jackfrancis]

/lgtm pending E2E

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, mboersma, tariq1890

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[codecov]

Codecov Report

Merging #31 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #31   +/-   ##
=======================================
  Coverage   46.89%   46.89%           
=======================================
  Files          91       91           
  Lines       13800    13800           
=======================================
  Hits         6471     6471           
  Misses       6721     6721           
  Partials      608      608