use curl in config mode if include and lib missing

[sbiscigl]

Issue #, if available:

issues/2717

Description of changes:

As mentioned in the issue

Right now it does not seem possible to use a custom build of Curl built with CMake when it is installed in Config mode.

which is true, as of the moment if you build curl from source the only way you can is by building it with autoconf. This changes to fall back to use curl by configuration if we cannot find the needed include or lib dirs from FindCURL.

Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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[pr0g]

Changes LGTM! 😄 Thanks for adding support for this 🥳