[Rust Server] Sort operations so that the ones with fewest params come first

[richardwhiuk]

In the generated Rust Server code, the order of the operations list determines the order of cases in a match statement.

This meant that if we had two operations (say, /foo/bar/ and /foo/{something}) where a given path (/foo/bar) could match both, it matched the operation whose operationId was alphabetically first, rather than following https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.3.md#pathsObject which says:

When matching URLs, concrete (non-templated) paths would be matched before their templated counterparts.

This sorts the operations so that the ones with fewest path parameters come first, which does meet that requirement.

This fix was contributed by @rkd-msw

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh ./bin/configs/*.yaml
  ./bin/utils/export_docs_generators.sh
  

  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.6.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

Rust Technical Committee: @frol @farcaller @paladinzh @jacob-pro