reduce spam on info log of cellular sockets

[LukasKarel]

Summary of changes

Reduce spam on information log of cellular stack.
Hide secrets on authentication.

Impact of changes

Migration actions required

Documentation

None

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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]

There's cmake error that might be on main (not related to this MR). I'll try to review it later.

This PR looks fine to me.