[MCP] Add support for streamable http servers with codex mcp add and replace bearer token handling (#4904)

1. You can now add streamable http servers via the CLI
2. As part of this, I'm also changing the existing bearer_token plain
text config field with ane env var

```
mcp add github --url https://api.githubcopilot.com/mcp/ --bearer-token-env-var=GITHUB_PAT
```

codex-rs/Cargo.lock

@@ -4772,9 +4772,9 @@ dependencies = [
 
 [[package]]
 name = "rmcp"
-version = "0.8.0"
+version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "583d060e99feb3a3683fb48a1e4bf5f8d4a50951f429726f330ee5ff548837f8"
+checksum = "6f35acda8f89fca5fd8c96cae3c6d5b4c38ea0072df4c8030915f3b5ff469c1c"
 dependencies = [
  "base64",
  "bytes",
@@ -4806,9 +4806,9 @@ dependencies = [
 
 [[package]]
 name = "rmcp-macros"
-version = "0.8.0"
+version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "421d8b0ba302f479214889486f9550e63feca3af310f1190efcf6e2016802693"
+checksum = "c9f1d5220aaa23b79c3d02e18f7a554403b3ccea544bbb6c69d6bcb3e854a274"
 dependencies = [
  "darling 0.21.3",
  "proc-macro2",