Update python_panel_service.proto file to remove Disconnect and change Connect to OpenPanel

[mikeprosserni]

What does this Pull Request accomplish?

This PR updates the proto file to remove the Disconnect() method, and rename the Connect() method to OpenPanel(). The panel and the tests are updated accordingly. Since there's no longer a Disconnect(), the panel no longer supports the with statement.

Why should this Pull Request be merged?

The .proto file needs to match the .proto file in ASW: https://ni.visualstudio.com/DevCentral/_git/ASW/pullrequest/961874

What testing has been done?

Ran the linter, mypy, and the tests.

[github-actions]

Test Results

10 files  ± 0  10 suites  ±0   6s ⏱️ ±0s
 6 tests  -  2   6 ✅  -  2  0 💤 ±0  0 ❌ ±0 
60 runs   - 20  60 ✅  - 20  0 💤 ±0  0 ❌ ±0 

Results for commit c34baf3. ± Comparison against base commit e0b567a.

This pull request removes 5 and adds 3 tests. Note that renamed tests count towards both.

tests.unit.test_python_panel_service_stub ‑ test___connect___gets_response
tests.unit.test_python_panel_service_stub ‑ test___disconnect___gets_response
tests.unit.test_streamlit_panel ‑ test___connected_panel___set_value___gets_same_value
tests.unit.test_streamlit_panel ‑ test___first_connect_fails___connect___gets_value
tests.unit.test_streamlit_panel ‑ test___with_panel___set_value___gets_same_value

tests.unit.test_python_panel_service_stub ‑ test___open_panel___gets_response
tests.unit.test_streamlit_panel ‑ test___first_open_panel_fails___open_panel___gets_value
tests.unit.test_streamlit_panel ‑ test___opened_panel___set_value___gets_same_value