make cellular event queue size configurable

[LukasKarel]

Summary of changes

Make event queue size of the cellulardevice configurable. The state machine crashes sometimes at my application because it cant add a new callback to the queue.

Impact of changes

Migration actions required

Documentation

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[x] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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[0xc0170]

Hi @LukasKarel ,

you need to update unittests , see the error here https://github.com/ARMmbed/mbed-os/actions/runs/6145924743/job/16674270974?pr=15454#step:5:581

[LukasKarel]

Hi @0xc0170

Should be fixed

[0xc0170]

Ci started

[mbed-ci]

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jenkins-ci/mbed-os-ci_build-cloud-example-ARM	✔️
jenkins-ci/mbed-os-ci_build-cloud-example-GCC_ARM	✔️
jenkins-ci/mbed-os-ci_unittests	✔️
jenkins-ci/mbed-os-ci_build-greentea-ARM	✔️
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jenkins-ci/mbed-os-ci_build-example-ARM	✔️
jenkins-ci/mbed-os-ci_build-example-GCC_ARM	✔️
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