RFR: Section on project maintenance [v4]

[Jesper Wilhelmsson]

> * New section on project maintenance
> * New infographics on push/defer during rampdown
> * Moved JDK Release Process section to follow the Release Note section
> * Minor fixes

Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:

  Additions from Simms

-------------

Changes:
  - all: https://git.openjdk.org/guide/pull/92/files
  - new: https://git.openjdk.org/guide/pull/92/files/f6aefa93..54ea3c36

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=guide&pr=92&range=03
 - incr: https://webrevs.openjdk.org/?repo=guide&pr=92&range=02-03

  Stats: 52 lines in 1 file changed: 47 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/guide/pull/92.diff
  Fetch: git fetch https://git.openjdk.org/guide pull/92/head:pull/92

PR: https://git.openjdk.org/guide/pull/92