Create /plans command

[DavertMik]

The command must be similar to runs https://github.com/testomatio/explorbot/blob/main/src/commands/runs-command.ts

It should work in CLI and TUI to

• list all existing plans
• show detailed tests for each plan
• suggest commands to run a specific test from a plan

So I could quickly run:

$ explorbot plans

1. Plan 1
2. Plan 2
3. Plan 3

$ explorbot plans 1

1. Test 1
2. Test 2
3. Test 3

Run test from this plan as:
explorbot test 1 --from-plan <plan_title.md>

$ explorbot test 1 --from-plan <plan_title.md>