Cellular: update doxygen and add attach CellularDevice.

[jarvte]

• updated doxygen to better match function behavior
• added method attach to CellularDevice. There are methods that are asynchronous but these was now callback possibility.

@AriParkkila please review

Pull request type

[X] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[0xc0170]

As we are still waiting for docs review, I would suggest one quick fix. Split this commit into two as stated

• add Callback functionality
• update doxygen

This helps reviewers (in this case docs team) to review only second commit for instance.

[jarvte]

Split in to 2 commits. Second commit has also one new doxygen comment which comes with new method.

[0xc0170]

@melwee01 Can you review?

[melwee01]

Will give it a look after lunch.

[mbed-ci]

Test run: FAILED

Summary: 5 of 7 test jobs failed
Build number : 1
Build artifacts
Build logs

Failed test jobs:

• jenkins-ci/mbed-os-ci_mbed2-build-GCC_ARM
• jenkins-ci/mbed-os-ci_mbed2-build-IAR
• jenkins-ci/mbed-os-ci_build-IAR
• jenkins-ci/mbed-os-ci_build-GCC_ARM
• jenkins-ci/mbed-os-ci_build-ARM

[0xc0170]

CI restarted (Aborted previously)

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 2
Build artifacts
Build logs

[0xc0170]

Waiting for docs team to approve, then ready for merge

[cmonr]

@ARMmbed/mbed-docs Feel free to do your thing.

If y'all need to copy-edit the PR, then that's fine. We can restart CI as needed.

[cmonr]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 11 of 11 test jobs passed
Build number : 3
Build artifacts