Update help string for 'update task-meta' and 'update launchplan-meta'

[katrogan]

TL;DR

See title, updates for correct usage.

Type

• Bug Fix
• Feature
• Plugin

Are all requirements met?

• Code completed
• Smoke tested
• Unit tests added
• Code documentation added
• Any pending items have an associated Issue

Complete description

How did you fix the bug, make the feature etc. Link to any design docs etc

Tracking Issue

https://github.com/flyteorg/flyte/issues/

Follow-up issue

NA
OR
https://github.com/flyteorg/flyte/issues/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8428367) 67.69% compared to head (3b348b7) 67.69%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #445   +/-   ##
=======================================
  Coverage   67.69%   67.69%           
=======================================
  Files         148      148           
  Lines        6622     6622           
=======================================
  Hits         4483     4483           
  Misses       1851     1851           
  Partials      288      288           

Flag	Coverage Δ
unittests	67.69% <ø> (ø)

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