Fix memory leak on stream load when updating CA Certificate

[sguarin]

Summary

This PR fix a memory leak when reconfiguring CA Certificate with multiple calls to WiFiClientSecure::setCACert()

Impact

When reconfiguring multiple times a CA certificate, or if your systems refresh the connection calling multiple times this function, the system will run out of memory.

Related links

#5826

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Unit Test Results

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Results for commit 1e962d3.

[mrengineer7777]

@VojtechBartoska The memory leak mentioned here is resolved in PR #6387.

I agree with adding _use_insecure = false; to setCACert(), setCertificate(), setPrivateKey(). setInsecure is used in setInsecure().

@me-no-dev setInsecure() is a dangerous function as it doesn't free memory allocated in loadCACert(). But....

Calling loadCACert() after setCACert() may free a pointer that doesn't belong to this module. In my opinion loadCACert(), loadCertificate(), loadPrivateKey() should all have their own private storage variables. Then call free() for each variable in setInsecure() and ~WiFiClientSecure().

[lucasssvaz]

Changes already implemented.