feat: gotemplate formatting for Dex config file

[nabokihms]

Signed-off-by: m.nabokikh [email protected]

Overview

• read config file as a template and execute it
• add sprig function support
• provide template configuration example

What this PR does / why we need it

An alternative of #1893
Instead of adding an external tool (dockerize), this PR introduces another approach.

Special notes for your reviewer

Does this PR introduce a user-facing change?

Add go template formatting support for Dex config file.

[sagikazarmark]

I'm very much against this approach. This shouldn't be Dex's responsibility. Dockerize indeed seems to be a dead end, so I see two ways ahead:

• Fork/rewrite dockerize: the community needs a project like this IMO anyway
• Try gotemplate (suggested in Add dockerize to the docker image #1838 (comment)): we don't use anything other than template generation.

[nabokihms]

Just an example, we can close this PR after figuring out the right way.

[nabokihms]

Personally, I'm more into gomplate, than rewriting dockerize (or rewriting anything).

• arm packages
• Crypto functions
• YAML formatting function
• Solid doccumentation

[sagikazarmark]

I think we can close this in favor of #1893