Add MXNet deprecation message to the docs and plugin

[JanuszL]

• adds MXNet deprecation message to the docs and plugin

Category:

Other (e.g. Documentation, Tests, Configuration)

Description:

• adds MXNet deprecation message to the docs and plugin

Additional information:

Affected modules and functionalities:

• MXNet plugin
• MXNet docs

Key points relevant for the review:

• wording

Tests:

• Existing tests apply
• New tests added
  • Python tests
  • GTests
  • Benchmark
  • Other
• N/A

Checklist

Documentation

• Existing documentation applies
• Documentation updated
  • Docstring
  • Doxygen
  • RST
  • Jupyter
  • Other
• N/A

DALI team only

Requirements

• Implements new requirements
• Affects existing requirements
• N/A

REQ IDs: N/A

JIRA TASK: N/A

[JanuszL]

!build

[dali-automaton]

CI MESSAGE: [14971844]: BUILD STARTED

[dali-automaton]

CI MESSAGE: [14971844]: BUILD PASSED

[JanuszL]