Let the build_arg_string function handle GMT configurations

[seisman]

Originally posted by @seisman in #2208 (comment)

When working on the Figure.timestamp function, I feel sometimes we may need to pass GMT's configurations directly to the GMT C API, i.e., passing a string like --FONT_LABEL=xxxx to the call_module function.

I propose to add a new parameter (e.g., confdict) to the build_arg_string function, which takes a dict and convert key-value pairs to the form of --key=value, e.g.,

build_arg_string(kwdict, confdict={"FONT_LOGO": font, "FORMAT_TIME_STAMP": timefmt}

[seisman]

Ping @GenericMappingTools/pygmt-maintainers for comments on this enhancement before I start to work on it.

[michaelgrund]

Ping @GenericMappingTools/pygmt-maintainers for comments on this enhancement before I start to work on it.

Sounds good from my side!

[weiji14]

Just to be clear, do you intend the --FONT_LABEL options to be internal only, or should users be allowed to do something like fig.timestamp(..., FONT_LABEL="xxxx")? By the way, this seems similar to what was discussed in #455.

[seisman]

do you intend the --FONT_LABEL options to be internal only, or should users be allowed to do something like fig.timestamp(..., FONT_LABEL="xxxx")?

It's only for internal use.

[weiji14]

do you intend the --FONT_LABEL options to be internal only, or should users be allowed to do something like fig.timestamp(..., FONT_LABEL="xxxx")?

It's only for internal use.

Ok, that sounds good.