Add IsTemplate option in create repo ui and api

[a1012112796]

As title

[codecov-commenter]

Codecov Report

Merging #12942 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #12942      +/-   ##
==========================================
- Coverage   42.82%   42.81%   -0.02%     
==========================================
  Files         661      661              
  Lines       72974    72977       +3     
==========================================
- Hits        31251    31244       -7     
- Misses      36654    36664      +10     
  Partials     5069     5069              

Impacted Files	Coverage Δ
models/repo.go	55.11% <ø> (ø)
modules/auth/repo_form.go	42.34% <ø> (ø)
modules/structs/repo.go	50.00% <ø> (ø)
modules/repository/create.go	52.72% <100.00%> (+0.87%)	⬆️
routers/api/v1/repo/repo.go	61.78% <100.00%> (+0.10%)	⬆️
routers/repo/repo.go	27.85% <100.00%> (+0.25%)	⬆️
models/unit.go	46.57% <0.00%> (-2.74%)	⬇️
modules/charset/charset.go	68.53% <0.00%> (-2.25%)	⬇️
services/gitdiff/gitdiff.go	72.85% <0.00%> (-1.64%)	⬇️
modules/log/file.go	73.60% <0.00%> (-1.61%)	⬇️
... and 5 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7a7f560...d1aa33e. Read the comment docs.