Merge bitcoin/bitcoin#31384: mining: bugfix: Fix duplicate coinbase tx weight reservation

386eecff5f doc: add release notes (ismaelsadeeq)
3eaa0a3b66 miner: init: add `-blockreservedweight` startup option (ismaelsadeeq)
777434a2cd doc: rpc: improve `getmininginfo` help text (ismaelsadeeq)
c8acd4032d init: fail to start when `-blockmaxweight` exceeds `MAX_BLOCK_WEIGHT` (ismaelsadeeq)
5bb31633cc test: add `-blockmaxweight` startup option functional test (ismaelsadeeq)
2c7d90a6d6 miner: bugfix: fix duplicate weight reservation in block assembler (ismaelsadeeq)

Pull request description:

  * This PR attempts to fix the duplicate coinbase weight reservation issue we currently have.
  * Fixes #21950

  We reserve 4000 weight units for coinbase transaction in `DEFAULT_BLOCK_MAX_WEIGHT`

  7590e93bc7/src/policy/policy.h (L23)

  And also reserve additional `4000` weight units in the default `BlockCreationOptions` struct.

  7590e93bc7/src/node/types.h (L36-L40)

  **Motivation**

  - This issue was first noticed during a review here https://github.com/bitcoin/bitcoin/pull/11100#discussion_r136157411)
  - It was later reported in issue #21950.
  - I also came across the bug while writing a test for building the block template. I could not create a block template above `3,992,000` in the block assembler, and this was not documented anywhere. It took me a while to realize that we were reserving space for the coinbase transaction weight twice.

  ---
  This PR fixes this by consolidating the reservation to be in a single location in the codebase.

  This PR then adds a new startup option `-blockreservedweight` whose default is `8000` that can be used to lower or increase the block reserved weight for block header, txs count, coinbase tx.

ACKs for top commit:
  Sjors:
    ACK 386eecff5f
  fjahr:
    Code review ACK 386eecff5f
  glozow:
    utACK 386eecff5f, nonblocking nits. I do think the release notes should be clarified more
  pinheadmz:
    ACK 386eecff5f

Tree-SHA512: f27efa1da57947b7f4d42b9322b83d13afe73dd749dd9cac49360002824dd41c99a876a610554ac2d67bad7485020b9dcc423a8e6748fc79d6a10de6d4357d4c

test/functional/test_framework/messages.py

@@ -33,6 +33,8 @@ from test_framework.util import assert_equal
 
 MAX_LOCATOR_SZ = 101
 MAX_BLOCK_WEIGHT = 4000000
+DEFAULT_BLOCK_RESERVED_WEIGHT = 8000
+MINIMUM_BLOCK_RESERVED_WEIGHT = 2000
 MAX_BLOOM_FILTER_SIZE = 36000
 MAX_BLOOM_HASH_FUNCS = 50