RFR: Section on project maintenance [v5]

[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:

  Fixes after reviews.

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Changes:
  - all: https://git.openjdk.org/guide/pull/92/files
  - new: https://git.openjdk.org/guide/pull/92/files/54ea3c36..b4ac25ab

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=guide&pr=92&range=04
 - incr: https://webrevs.openjdk.org/?repo=guide&pr=92&range=03-04

  Stats: 42 lines in 1 file changed: 26 ins; 2 del; 14 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