clang-tidy: adding "--clang-tidy-config=<file-path>" to specify custom config file (was RE: clang-tidy -- using custom path config file)

Thanks James for your suggestions.

I have raised review request for adding support of '--clang-tidy-config=<file-path>'.

Review request is -- ⚙ D89936 [clang-tidy] adding "--config-file=<file-path>" to specify custom config file.

<patch_summary>
clang-tidy: adding "--clang-tidy-config=<file-path>" to specify custom config file.

Let clang-tidy to read config from specified file.
Example:
$ clang-tidy --clang-tidy-config=/some/path/myTidyConfig --list-checks --
   ...this will read config from '/some/path/myTidyConfig'.

May speed-up tidy runtime since now it will just look-up <file-path>
instead of searching ".clang-tidy" in parent-dir(s).

Directly specifying config path helps setting build dependencies.
</patch_summary>

As suggested in patch submission page (via git blame), I have also added Alexander Kornienko, Haojian Wu, Dmitry Polukhin and you.
Please let me know if I missed to add any other person in reviewer's list.

Thank you in advance for your kind review.
-Hiral