feat: Add stats support for basic operations

[nishkrishnan]

This implementation uses tally, an OSS library for emitting stats. This implementation supports only statsd currently, however since this lib supports other stats providers (like prometheus) it's relatively straightforward to add support in atlantis for it.

To configure statsd, you can do so via the server config yaml:

ie.

metrics:
  statsd:
    host: '127.0.0.1'
    port: '8125'

Note: this is copied from the lyft fork, hence the large PR. This works internally in production.

TODO:

• Add docs on this

[majormoses]

LGTM though I wont pretend I am good with golang.

[majormoses]

Should this also be lowercase?

Suggested change

	func (j *JobsController) GetProjectJobs(w http.ResponseWriter, r *http.Request) {
	func (j *JobsController) getProjectJobs(w http.ResponseWriter, r *http.Request) {

[nishkrishnan]

no, these should be exported ideally to represent that only this function should be called since it has stats associated with it.

[majormoses]

Should this be lowercase?

Suggested change

	func (j *JobsController) GetProjectJobsWS(w http.ResponseWriter, r *http.Request) {
	func (j *JobsController) getProjectJobsWS(w http.ResponseWriter, r *http.Request) {

[marceloboeira]

@nishkrishnan if I add:

metrics:
  statsd:
    host: '127.0.0.1'
    port: '8125

to my atlantis yaml it breaks it:

Error: initializing server: parsing atlantis.yaml file: yaml: unmarshal errors:
  line 6: field metrics not found in type raw.GlobalCfg

[evanstachowiak]

@nishkrishnan if I add:

metrics:
  statsd:
    host: '127.0.0.1'
    port: '8125

to my atlantis yaml it breaks it:

Error: initializing server: parsing atlantis.yaml file: yaml: unmarshal errors:
  line 6: field metrics not found in type raw.GlobalCfg

@marceloboeira you're missing a closing single-quote on your port: line.