Allow to build Minimal firmware with TLS support

[bkmit]

Description:

Do not undefine USE_MQTT_TLS by force for MINIMAL firmware.
This PR do not change any defaults.

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR.
• The code change is tested and works on core 2.6.1
• The code change pass travis tests. Your PR cannot be merged unless tests pass
• I accept the CLA.

[ascillato]

Sorry, Minimal firmware is not for normal usage. It is a super small version to be used just in the UPDATING process. The minimal firmware will stay in your device for just few seconds while it is updating to your full version. Adding this option will increase minimal size, restricting the available free space for the full version.

[bkmit]

This works perfectly for me. I know what purpose of minimal was created for.
This patch do not change current project build defines, only allow to define USE_MQTT_TLS in user_config_override.h or platfomio_override.ini files if user (like me) need to.
I am using custom built TLS-enabled minimal image to do MQTT only management of all my modules.
Hope this explain why I have created this PR.

[ascillato2]

MQTT only management of all my modules.

@bkmit Bohdan, ok, you have a valid point.

@arendst Theo, what do you think?

[ascillato]

@bkmit Bohdan,

Thanks for sharing 👍