Add Option to globally disable apply

[gezb]

Implement a new server flag that will disable the ability to run atlantis apply, as suggested in #1219

[codecov]

Codecov Report

Merging #1230 into master will increase coverage by 0.02%.
The diff coverage is 82.60%.

@@            Coverage Diff             @@
##           master    #1230      +/-   ##
==========================================
+ Coverage   69.95%   69.98%   +0.02%     
==========================================
  Files          71       71              
  Lines        5362     5380      +18     
==========================================
+ Hits         3751     3765      +14     
- Misses       1263     1265       +2     
- Partials      348      350       +2     

Impacted Files	Coverage Δ
cmd/server.go	79.09% <ø> (ø)
server/events_controller.go	56.07% <ø> (ø)
server/user_config.go	100.00% <ø> (ø)
server/events/command_runner.go	50.87% <60.00%> (+0.16%)	⬆️
server/events/comment_parser.go	93.98% <81.81%> (-1.18%)	⬇️
server/events/markdown_renderer.go	92.20% <100.00%> (+0.10%)	⬆️
server/server.go	61.34% <100.00%> (+0.30%)	⬆️

---

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 c789e1a...aeb6c50. Read the comment docs.

[lkysow]

Thanks for the PR! It looks super good. Can you also update the website flag docs?

[gezb]

@lkysow I have addressed your comments and pushed my changes

One issue I see now is the fact that we will not be able to plan multiple PR's because of the locking. I see there is #1212 been raised would this be best as another feature/server-flag that can be used alongside --disable-apply?

I would not look to remove locking but if the flag is enabled unlock the repo automatically once the plan has completed allowing other plans to be run?

[lkysow]

Getting close, thanks for the attention to detail.

[gezb]

I have addressed the last round of comments and re-based, I have left one review comment unresolved as I am not sure how I proceed with that one