docs: document project Maintainer emeritus process

[jpower432]

Objective
This change documents the maintainer lifecycle proceduces for project Maintainers.

Note: the Oversight Commitee lifecycle procedures are out of scope

Related Issues

Closes #59
Closes #127

Requirements: Per our governance documentation, this update requires a majority vote of the Oversight Committee

Need clarification on whether supermajority is needed. This remove a section of the Governance process so it may be super majority.

Significant Decisions/Changes

• Maintainer can self nominate - Incorporates docs: update MEMBERSHIP.md to allow maintainers to self nominate #132
• Inactivity timeframe is reduced to 6 months from 12 to match project velocity requirements
• Specific project Maintainer process (how we execute what is in the GOVERNANCE.md at the subproject level) information in added in MAINTAINER_GUIDELINES

[jpower432]

@vikas-agarwal76 Can we continue the MEMBERSHIP.md disucssion here? My intent with MAINTAINER_GUIDELINES.md was to go into more detail on the processes and have the MEMBERSHIP.md clearly define what the roles are and how they are documented. I don't have a strong opinion on having separate or a single document.

[vikas-agarwal76]

PR #135 closes this.