[chore] add container parser in the list of stanza operators (#33091)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->

This PR adds the `container` parser operator in the list of the
supported stanza operators.

**Link to tracking Issue:** <Issue number if applicable>

**Testing:** <Describe what testing was performed and which tests were
added.>

**Documentation:** <Describe the documentation added.>

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

Author: ChrsMark

pkg/stanza/docs/operators/README.md

@@ -27,6 +27,7 @@ Parsers:
 - [trace_parser](./trace_parser.md)
 - [uri_parser](./uri_parser.md)
 - [key_value_parser](./key_value_parser.md)
+- [container](./container.md)
 
 Outputs:
 - [file_output](./file_output.md)