chore: update dependencies to latest versions (#56)

- Update `firebase.google.com/go/v4` to v4.14.1
- Update `golang.org/x/oauth2` to v0.21.0
- Update `google.golang.org/api` to v0.183.0
- Update `cloud.google.com/go` to v0.114.0 (indirect)
- Update `cloud.google.com/go/auth` to v0.5.1 (indirect)
- Update `github.com/go-logr/logr` to v1.4.2 (indirect)
- Update `go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc` to v0.52.0 (indirect)
- Update `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp` to v0.52.0 (indirect)
- Update `go.opentelemetry.io/otel` to v1.27.0 (indirect)
- Update `go.opentelemetry.io/otel/metric` to v1.27.0 (indirect)
- Update `go.opentelemetry.io/otel/trace` to v1.27.0 (indirect)
- Update `golang.org/x/crypto` to v0.24.0 (indirect)
- Update `golang.org/x/net` to v0.26.0 (indirect)
- Update `golang.org/x/sys` to v0.21.0 (indirect)
- Update `golang.org/x/text` to v0.16.0 (indirect)
- Update `google.golang.org/genproto` to v0.0.0-20240604185151-ef581f913117 (indirect)
- Update `google.golang.org/genproto/googleapis/api` to v0.0.0-20240604185151-ef581f913117 (indirect)
- Update `google.golang.org/genproto/googleapis/rpc` to v0.0.0-20240604185151-ef581f913117 (indirect)

Signed-off-by: Bo-Yi Wu <[email protected]>

docs: refactor tests and clean up codebase

- Convert bullet points in README.md to a list format
- Remove unused import statements
- Rename `Test_sendGoogleNotification_Success` to `TestMockClient`
- Simplify mock server response in test
- Refactor client initialization in test
- Add `checkSuccessfulBatchResponseForSendEach` function to validate response in test

Signed-off-by: Bo-Yi Wu <[email protected]>

feat: enable HTTP request/response logging in debug mode (#50)

- Add `debug` field to `Client` struct
- Initialize `httpClient` with `debugTransport` if `debug` mode is enabled
- Create `debug.go` to define `debugTransport` for logging HTTP requests and responses
- Add `WithDebug` option to configure debug mode in `option.go`

Signed-off-by: appleboy <[email protected]>

chore(http): refactor authentication to use oauth2 library (#49)

- Replace `google.golang.org/api/transport` with `golang.org/x/oauth2/google`
- Add `credentialsJSON` field to `Client` struct
- Use `google.CredentialsFromJSON` instead of `transport.Creds`
- Add error handling for reading credentials file in `WithCredentialsFile`
- Store credentials JSON data in `Client` struct in `WithCredentialsFile` and `WithCredentialsJSON`
- Rename parameter `json` to `data` in `WithCredentialsJSON` function

Signed-off-by: appleboy <[email protected]>

refactor: refactor codebase to improve maintainability

- Remove the `WithCustomClientOption` function and its associated comments

Signed-off-by: appleboy <[email protected]>

test: improve `TestUnmarshal` readability and accuracy

- Replace `reflect.DeepEqual` with detailed field-by-field comparison in `TestUnmarshal`
- Refactor multiline slice initialization to single line in `TestUnmarshal`

Signed-off-by: Bo-Yi Wu <[email protected]>

docs: refactor README for Current Tooling Usage

- Update the build status badge in README from Drone CI to GitHub Actions
- Remove instructions for fetching the package with `govendor` from README

Signed-off-by: Bo-Yi Wu <[email protected]>

chore(makefile): remove GOPACKAGE variable

chore: add go version in module

feat: support go module