Simplify theme command environment paths

[EvilGenius13]

WHY are these changes introduced?

Follow up to #5954 (comment)

We can further simplify the codepaths that a theme command can go through.

WHAT is this pull request doing?

In both no environment and single environment scenarios, they both make a session and then run the command. They are now lumped together based on what the environments variable has.

How to test your changes?

• Pull down the branch
• Build the branch
• Run a series of commands
  • shopify theme list
  • shopify theme list -e mystore
  • shopify theme list -e mystore -e myotherstore
• Ensure commands output the proper store(s)

Measuring impact

How do we know this change was effective? Please choose one:

• n/a - this doesn't need measurement, e.g. a linting rule or a bug-fix
• Existing analytics will cater for this addition
• PR includes analytics changes to measure impact

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes

[github-actions]

Coverage report

St.❔	Category	Percentage	Covered / Total
🟡	Statements	78.32% (+0.01% 🔼)	12542/16013
🟡	Branches	72.5% (+0.03% 🔼)	6105/8421
🟡	Functions	78.47%	3272/4170
🟡	Lines	78.77% (+0.01% 🔼)	11867/15066

Show files with reduced coverage 🔻

St.❔	File	Statements	Branches	Functions	Lines
🔴	... / theme-command.ts	38.78% (-4.62% 🔻)	12.5% (-6.73% 🔻)	40%	42.22% (-4.72% 🔻)

Test suite run success

2902 tests passing in 1259 suites.

Report generated by 🧪jest coverage report action from d45304d