feat(alerting): implement Gitea alerting provider (#842)

* feat: implement Gitea alerting provider integration

- Add TypeGitea for the gitea alerting provider
- Introduce a new file for the gitea alerting provider implementation
- Implement the AlertProvider struct with necessary fields for gitea integration
- Add validation logic for the AlertProvider configuration
- Create tests for the AlertProvider's validation and sending functionality
- Update go.mod to include the gitea SDK as a dependency
- Modify the alerting configuration validation to recognize TypeGitea

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* chore: integrate Gitea alerting provider configuration

- Add Gitea alerting provider import to the configuration file
- Update the comment for the RepositoryURL field to reflect Gitea instead of GitHub

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* feat: add Assignees support to AlertProvider functionality

- Add a field for Assignees to the AlertProvider struct
- Update the Send function to include Assignees in the alert payload

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* feat: implement Gitea alerting configuration and documentation

- Add a new image asset for Gitea alerts
- Update the README to include configuration details for Gitea alerts
- Introduce parameters for Gitea alerting, including repository URL and personal access token
- Document the behavior of the Gitea alerting provider regarding issue creation and resolution
- Include an example YAML configuration for Gitea alerts

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* Update README.md

Co-authored-by: TwiN <twin@linux.com>

* Update README.md

Co-authored-by: TwiN <twin@linux.com>

* Update README.md

Co-authored-by: TwiN <twin@linux.com>

* feat: refactor AlertProvider for improved client configuration

- Add import for the Gatus client library
- Remove the SkipVerify field from the AlertProvider struct
- Introduce ClientConfig field in the AlertProvider struct for client configuration
- Update validation logic to check for ClientConfig instead of SkipVerify

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* Update README.md

Co-authored-by: TwiN <twin@linux.com>

* chore: update configuration for Gitea integration

- Change references from GitHub to Gitea in the configuration section
- Update alerting provider descriptions to reflect the correct platform
- Swap the order of GitHub and Gitea configurations
- Replace Gitea alert image with GitHub alert image
- Adjust the type field from gitea to github in the relevant sections

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* fix: ensure ClientConfig is validated and defaults set

- Add a check for nil ClientConfig in the IsValid function
- Set ClientConfig to a default configuration if it is nil

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

---------

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Co-authored-by: TwiN <twin@linux.com>

go.mod

@@ -3,6 +3,7 @@ module github.com/TwiN/gatus/v5
 go 1.22.2
 
 require (
+	code.gitea.io/sdk/gitea v0.19.0
 	github.com/TwiN/deepmerge v0.2.1
 	github.com/TwiN/g8/v2 v2.0.0
 	github.com/TwiN/gocache/v2 v2.2.2
@@ -38,8 +39,10 @@ require (
 	github.com/blend/go-sdk v1.20220411.3 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/davidmz/go-pageant v1.0.2 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/go-fed/httpsig v1.1.0 // indirect
 	github.com/go-jose/go-jose/v4 v4.0.2 // indirect
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
@@ -49,6 +52,7 @@ require (
 	github.com/google/go-querystring v1.1.0 // indirect
 	github.com/google/s2a-go v0.1.7 // indirect
 	github.com/googleapis/enterprise-certificate-proxy v0.3.2 // indirect
+	github.com/hashicorp/go-version v1.6.0 // indirect
 	github.com/hashicorp/golang-lru/v2 v2.0.7 // indirect
 	github.com/jmespath/go-jmespath v0.4.0 // indirect
 	github.com/klauspost/compress v1.17.8 // indirect