Lint(RPaaS) deprecation notes

Before deprecating Lint(RPaaS) we did some investigating and discovered that the tool currently does not do much. Sampled failures were primarily due to pipeline issues (e.g. git not being able to connect to GitHub, agent issues, etc.).

A small subset of issues amounted to an error on PRs targeting `RPSaaSMaster` for `readme.md` files that specify an `openapi-subtype` that isn't `rpaas` or `provderHub`. (This validation is not done by autorest, it is done specifically in the Lint(RPSaaS) tool.)

The Lint(RPaaS) tool may then run `autorest` with an `openApiType` of `undefined` and `rpaasLint` of `true` which results in calling of `autorest` with `--openapi-type` equal to that defined in the `readme.md` file and NO `--openapi-subtype`.

The Lint(RPaaS) tool then filters all outputs for `RPaaSViolation` and logs and returns results.

At this point, there are [2 legacy](https://github.com/search?q=repo%3AAzure%2Fazure-openapi-validator%20RPaaSViolation&type=code) rules matching that category.

Start by locating the Lint(RPaaS) entry point and tracing its readme.md handling, autorest invocation, and RPaaSViolation filtering. Review the two legacy rules referenced in the issue and the RPSaaSMaster pipeline context. Done is not defined here; clarify whether deprecation means removing the tool, its validation, or only documenting the two remaining rules.

Written by the indexing model from the issue text.