Truly disabled profiler in prod
[FrameworkBundle] added a way to disable the profiler

Before:

  enabled: true  # the profiler is enabled and data are collected

  enabled: false # the profiler is enabled but data are not collected (data can be collected on demand)

  No way to disable the profiler

After:

  enabled: true  # the profiler is enabled and data are collected
  collect: true

  enabled: true  # the profiler is enabled but data are not collected (data can be collected on demand)
  collect: false

  enabled: false # the profiler is disabled
fixed the registration of the web profiler when the profiler is disabled
merged branch fabpot/profiler-activation (PR #7859)

This PR was merged into the master branch.

Discussion
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Profiler activation

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7064, #7071
| License       | MIT
| Doc PR        | symfony/symfony-docs#2565

As stated in #7071, there is no way to disable the profiler completely. Even when the `enabled` flag is set to `false`, the profiler is still registered but the data collectors are not activated.

Now, when `enabled` is `false`, the profiler is disabled. To get the old `false` behavior, you now need to set `enabled` to `true` and set the new `collect` flag to `false`.

Todo:

 - [x] update docs
 - [x] update Symfony SE -- not needed

Commits
-------

88ebd62 fixed the registration of the web profiler when the profiler is disabled
a11f901 [FrameworkBundle] added a way to disable the profiler
f675dd8 Truly disabled profiler in prod