Add OAS contract monitoring support (#325)

* Add OAS contract monitoring support

* Pass the contract failure reason to UI

* Fix the issues related to contract validation

* Fix rest of the issues in the UI

* Add documentation related to contract monitoring feature

* Fix a typo in the docs

* Unmarshal to `HTTPRequestResponsePair` only if the OAS validation is enabled

* Fix an issue caused by the merge commit

* Slightly change the logic in the `validateOAS` method

Change the `contractText` value to `No Breaches` or `Breach` and make the text `white-space: nowrap`.

* Retrieve and display the failure reason for both request and response

Also display the content of the contract/OAS file in the UI.

* Display the OAS under `CONTRACT` tab with syntax highlighting

Also fix the styling in the entry feed.

* Remove `EnforcePolicyFileDeprecated` constant

* Log the other errors as well

* Get context from caller instead

* Define a type for the contract status and make its values enum-like

* Remove an unnecessary `if` statement

* Validate OAS in the CLI before passing it to Agent

* Get rid of the `github.com/ghodss/yaml` dependency in `loadOAS` by using `LoadFromData`

* Fix an artifact from the merge conflict

agent/pkg/rules/rulesHTTP.go

@@ -46,7 +46,7 @@ func ValidateService(serviceFromRule string, service string) bool {
 
 func MatchRequestPolicy(harEntry har.Entry, service string) (resultPolicyToSend []RulesMatched, isEnabled bool) {
 	enforcePolicy, err := shared.DecodeEnforcePolicy(fmt.Sprintf("%s/%s", shared.RulePolicyPath, shared.RulePolicyFileName))
-	if err == nil {
+	if err == nil && len(enforcePolicy.Rules) > 0 {
 		isEnabled = true
 	}
 	for _, rule := range enforcePolicy.Rules {