feat(espp-rtsp): use espp::RtspClient

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Description

• Moved RtspClient into espp submodule and use that
• Updated main code accordingly

Motivation and Context

Using the submodule helps ensure the client and server stay in sync as changes come.

How has this been tested?

Building and running the main code. See also esp-cpp/espp#58

Screenshots (if appropriate, e.g. schematic, board, console logs, lab pictures):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update
• Hardware (schematic, board, system design) change
• Software change

Checklist:

• My change requires a change to the documentation.
• I have added / updated the documentation related to this change via either README or WIKI

Software

• I have added tests to cover my changes.
• I have updated the .github/workflows/build.yml file to add my new test to the automated cloud build github action.
• All new and existing tests passed.
• My code follows the code style of this project.

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Related to #1