Wire up --context CLI flag

[tchetwin]

Fixes #3121

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

#3121

Description

It looks like --context was not wired up in mergeOptions. Using the createGetOption helper to check both the config and command line options.

[codecov]

Codecov Report

Merging #3134 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3134      +/-   ##
==========================================
+ Coverage   89.28%   89.32%   +0.03%     
==========================================
  Files         165      165              
  Lines        5732     5732              
  Branches     1741     1741              
==========================================
+ Hits         5118     5120       +2     
+ Misses        380      379       -1     
+ Partials      234      233       -1

Impacted Files	Coverage Δ
src/utils/mergeOptions.ts	90.47% <ø> (+2.38%)	⬆️

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[lukastaegert]

Looks perfect, thanks!