Add find-ccache.sh with find_ccache_and_export_vars

[eramongodb]

Followup to https://github.com/mongodb/mongo-c-driver/pull/1522. Verified by this patch.

This PR proposes three sets of changes:

Remove ccache 3.4.3 detection

After recent updates to our EVG config to migrate to newer and recommended distros, none of the distros we currently use in our EVG config appear to provide a ccache version that fails this condition. Therefore, the workaround is removed for simplification purposes.

Remove CCache.cmake

This PR proposes moving the routines to opt-into ccache out of the CMake config and into our EVG scripts instead. CMake 3.17 introduced the CMAKE_<LANG>_COMPILER_LAUNCHER environment variables as a convenient, non-intrusive method of enabling ccache. Pre-3.17 CMake (i.e. in the build-and-test-with-toolchain tasks, which uses 3.1.0 (should we update this to 3.15?)) will simply ignore the env vars without emitting "manually-specified variables were not used by the project" warnings as would be the case when -D is used. Since most of our EVG scripts use a "latest" version of CMake (currently set to 3.25.3), most of our EVG tasks will correctly take advantage of these env vars when set.

This change is motivated by a CMake principle of keeping the config as simple as possible (this PR removes the custom MONGO_USE_CCACHE option), instead utilizing supported CMake configuration variables whenever able to minimize making assumptions about the user environment. (Ultimately, we should move the env vars and -D flags into dedicated CMake toolchain files for use on EVG.) If instead we want to keep ccache detection routines in the CMake configuration rather than using env vars (the status quo, i.e. for user convenience), this change can be reverted.

Add find-ccache.cmake

The repetition of setting ccache variables to support reuse of compilation results across different build directories + ccache detection motivated the addition of a find-ccache.cmake script (a la find-cmake-latest.sh). The find_ccache_and_export_vars() conveniently performs both a simple search for a ccache binary and the exporting of all necessary ccache-related environment variables (for both CMake and ccache itself).

The find_ccache() function is motivated by the realization that some of the distros we test on, despite not providing a system-installed ccache binary, do provide ccache via the MongoDB server toolchain instead (which is present on many non-Windows distros, with the caveat that there are no guarantees of stability/support for non-server teams). This function therefore helps slightly extend the set of distros where we can take advantage of ccache. (Note: extending ccache availability to Windows distros is requested in DEVPROD-4074.) Note the odd use of || and true is to avoid potential interference by set -o errexit.