This PR introduces a script and some templates to use the prdoc involved
in a release and build:
- the changelog
- a simple draft of audience documentation

Since the prdoc presence was enforced in the middle of the version
1.5.0, not all PRs did come with a `prdoc` file.
This PR creates all the missing `prdoc` files with some minimum content
allowing to properly generate the changelog.
The generated content is **not** suitable for the audience
documentation.

The audience documentation will be possible with the next version, when
all PR come with a proper `prdoc`.

## Assumptions

- the prdoc files for release `vX.Y.Z` have been moved under
`prdoc/X.Y.Z`
- the changelog requires for now for the prdoc files to contain author +
topic. Thos fields are optional.

The build script can  be called as:
```
VERSION=X.Y.Z ./scripts/release/build-changelogs.sh
```

Related:
-  #1408

---------

Co-authored-by: EgorPopelyaev <egor@parity.io>

## Overview

This PR aligns the `spec_version` formatting to the [recent
changes](https://github.com/polkadot-fellows/runtimes/pull/26/files#diff-efa4caeb17487ecb13d8f5eb7863c3241d84afa2e73fbf25909a2ca89df0f362R142)
made for the Polkadot/Kusama runtimes.

It also backports the latest version `v1.4.0` bumps as `1_004_000`.

## Details

During the switch from `v0.9` to `v1.x`, the format of the
`spec_version` was modified from: `(M)m_ppp` for a runtime considered on
version `M.m.pp`. For instance `0.9.42` had a `spec_version` of `9420`.

With the transition to `v1.x`, the format was changed to a bigger number
(still `u32`) formatted as `MM_mm_ppp` where `1.2.3` would be stored as
`01_02_003`.

This PR aligns the format with that has been introduced in the
fellowship repo: `MMM_mmm_ppp`.

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

Add collectives and glutton parachain westend runtimes to prepare for
#1737.

The removal of system parachain native runtimes #1737 is blocked until
chainspecs and runtime APIs can be dealt with cleanly (merge of #1256
and follow up PRs).

In the meantime, these additions are ready to be merged to `master`, so
I have separated them out into this PR.

Also marked `bridge-hub-westend` as unimplemented in line with [this
issue](https://github.com/paritytech/parity-bridges-common/issues/2602).

TODO
- [x] add to `command-bot` benchmarks
- [x] add to `command-bot-scripts` benchmarks
- [x] generate weights

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Muharem <ismailov.m.h@gmail.com>
Co-authored-by: command-bot <>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Branislav Kontur <bkontur@gmail.com>