Add stability as a separate column in Markdown tables

[lmolkova]

Follow-up on #272

This PR

• moves stability to a dedicated column for supported md tables (attributes and metrics).
• [BREAKING] changes cmd line args controlling rendering:
  • badges were opt-in per stability (--md-enable-stable), now they are opt-out per stability level (--md-disable-stable-badge)
  • default has changed from not rendering badges to rendering them
  • there is no way to opt-out from generating stability column (the default was to not render it at all)

Example:

Attribute	Type	Description	Examples	Requirement Level	Stability
test.deprecated_experimental_attr	boolean			Required	Removed.
test.deprecated_stable_attr	boolean			Required	Removed.
test.exp_attr	boolean			Required
test.stable_attr	boolean			Required

Name	Instrument Type	Unit (UCUM)	Description	Stability
stable_metric	Histogram	s	stable_metric

Name	Instrument Type	Unit (UCUM)	Description	Stability
experimental_metric	Counter	{e}	experimental_metric

Name	Instrument Type	Unit (UCUM)	Description	Stability
deprecated_metric	UpDownCounter	{d}	deprecated_metric	Removed.

[arminru]

Looks great! Thank you