build: Add cfl-static as a TARGETS

[cosmo0920]

This is because system installation with deb/rpm packages should include libcfl-static.a for correct linking for cmetrics library.

Otherwise, when system OK is displayed in configuration phase, libcfl-static.a linking should be failed.

[edsiper]

why packaging systems needs the static library ?, cfl should be bundled by default inside the main cmetrics library

[cosmo0920]

When installing cmetrics library as a package, libcfl-static.a is also needed to bundle cmetrics.deb or cmetrics.rpm.
fluent-otel-proto, mpack and xxhash are also installed as libraries when packaging:
https://github.com/fluent/cmetrics/blob/master/CMakeLists.txt#L277
https://github.com/fluent/cmetrics/blob/master/CMakeLists.txt#L218
https://github.com/fluent/cmetrics/blob/master/CMakeLists.txt#L254

In addition, this library targets are only installed when enabling CMT_INSTALL_TARGETS option is turned on.

Just developing fluent-bit and its related software in C, this issue shouldn't encounter.
But, when developing calyptia-plugin or cmetrics-go, we need to install cmetrics as a DEB or RPM package to load cmetrics functionalities.

[edsiper]

thanks for the explanation, so if CMT_INSTALL_TARGETS is needed all good