RFR: Section on project maintenance [v2]

[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:

  Update src/guide/project-maintenance.md
  
  Co-authored-by: Ludvig Janiuk <ludvig.janiuk at gmail.com>

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

Changes:
  - all: https://git.openjdk.org/guide/pull/92/files
  - new: https://git.openjdk.org/guide/pull/92/files/c1fb601b..e2b24604

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=guide&pr=92&range=01
 - incr: https://webrevs.openjdk.org/?repo=guide&pr=92&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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