feat: add support for insecure mode in Gitea client configuration (#20)

- Add `GITEA_INTERACTIVE` configuration example in README files
- Add `insecure` flag to ignore TLS certificate errors in `cmd.go`
- Set insecure mode based on `GITEA_INSECURE` environment variable in `cmd.go`
- Add `Insecure` boolean variable in `pkg/flag/flag.go`
- Import `crypto/tls` and `net/http` in `pkg/gitea/gitea.go`
- Modify Gitea client creation to support insecure HTTP client in `pkg/gitea/gitea.go`

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

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/20
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Co-committed-by: Bo-Yi Wu <appleboy.tw@gmail.com>

README.md

@@ -109,6 +109,7 @@ To configure the MCP server for Gitea, add the following to your MCP configurati
       ],
       "env": {
         // "GITEA_HOST": "https://gitea.com",
+        // "GITEA_INTERACTIVE": "true",
         "GITEA_ACCESS_TOKEN": "<your personal access token>"
       }
     }