Read config from ~/.rid

[awakia]

Why

we want to use command like rid pg or rid es anywhere without adding rid-pg / rid-es to every ripository

What

to solve that problem, this PR

• enables to read substitution command from ~/.rid/libexec
• enables to run such rid command (which runs outside of container) without configfile

the problem here is it is hard to write test.
@creasty please take a look?

[codecov]

Codecov Report

Merging #15 into master will decrease coverage by 2.63%.
The diff coverage is 26.66%.

@@            Coverage Diff             @@
##           master      #15      +/-   ##
==========================================
- Coverage   57.21%   54.58%   -2.64%     
==========================================
  Files           4        4              
  Lines         194      240      +46     
==========================================
+ Hits          111      131      +20     
- Misses         74       98      +24     
- Partials        9       11       +2

Impacted Files	Coverage Δ
cli/cli.go	52.21% <0%> (-2.89%)	⬇️
project/context.go	56.16% <36.36%> (-1.53%)	⬇️
util/util.go	53.33% <0%> (-5.93%)	⬇️
project/config.go	62.5% <0%> (-2.21%)	⬇️

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