…ce id generation for buses (nicolas-grekas)

This PR was merged into the 4.1-dev branch.

Discussion
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[FrameworkBundle][Messenger] Remove convention-based service id generation for buses

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes (DX)
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Service ids for buses are user facing ids: ppl *will* have to deal with them when wiring their services.
Like for cache pools, we should ask ppl to declare them using full identifiers, instead of having a convention-based way to turn a name into and id (which is something nobody will be able to remember at some point.)

Commits
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c7a0045 [FrameworkBundle][Messenger] Remove convention-based service id generation for buses

This PR was merged into the 4.1 branch.

Discussion
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[Messenger] Fix default bus name

| Q             | A
| ------------- | ---
| Branch?       | 4.1 <!-- see below -->
| Bug fix?      | yesish
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #27162   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | N/A

After #27162, the default bus name configured automatically should use a full service id too, otherwise we currently get a `default` service id, no namespace identifier, which is the default bus.

Commits
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fa9b984 [Messenger] Fix default bus name

This PR was submitted for the master branch but it was squashed and merged into the 4.1 branch instead (closes #9727).

Discussion
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[Messenger] Update the messenger documentation

- [x] Fixes #9641 with the middleware configuration.
- [x] Fixes #9617 with the multiple bus configuration.
- [x] Change adapters to transports (waiting merge: symfony/symfony#27129)
- [x] middlewares config entry is renamed middleware (symfony/symfony#27177)
- [x] in the config, message buses names are the full service id you'll use (symfony/symfony#27162)
- [x] Add TransportInterface as first class citizen sender+receiver (symfony/symfony#27164)

Commits
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c3c3528 Few updates following review
64bfd75 Change wording and don't use `.`-based services so it's just clearer
e1f3b5a Fix the formating of the method name
9b7b85f Update the example of using multiple buses to use DI's `bind`s
c76b2c2 Uses the full service name when configuring the buses from the YAML configuration
2409798 Middleware does not have a plural
a20286d Add a note about the symfony serializer pack
10f46eb Introduce the `TransportInterface`
ef70bc0 Add a documentation about the middlewares
3ff8cfe Add multiple buses configuration and type-hint example
a4bc592 Rename the adapters to transport