Update `SpringBootContextLoader` so that when possible the
`SpringApplication` remains in control of creating the `Environment`
instance.
Prior to this commit, we would always create the `Environment` in the
`SpringBootContextLoader` and then call `setEnvironment` on the
`SpringApplication`. This meant that the `ApplicationEnvironment`
classes were not used and that `isCustomEnvironment` was set to `true`
so no conversion was applied.
With the updated code, an `ApplicationListener` is used to mutate the
`Environment` instance and add the required test property sources.
Fixes gh-29169
We've seen some problems, particularly on CI, where Embedded Mongo
hangs while trying to start the Mongo process. To limit the problem,
this commit replaces the use of Embedded Mongo with Testcontainers
where we can, leaving Embedded Mongo in use only where we're
specifically testing our Embedded Mongo support.
Closes gh-28843
Refine the logic introduced in 64270eca to use a side-effect free
Environment implementation rather than converting the Environment early.
Early conversion can cause condition evaluation issues if
`src/test/resources/application.properties` files are bound to the
`SpringApplication`. Specifically the `spring.main.web-application-type`
property can change the `Environment` type which must happen before
conditions are evaluated.
Fixes gh-29169
Update `launch.script` so that the `run_user` variable is only set when
the user actually exists. Prior to this commit, if the jar file was
owned by a non-existing user the startup script could fail.
Fixes gh-29370