Clean up opentracing configuration options (#5712)

Clean up config settings and dead code.

This is mostly about cleaning up the config format, to bring it into line with our conventions. In particular:
 * There should be a blank line after `## Section ##' headings
 * There should be a blank line between each config setting
 * There should be a `#`-only line between a comment and the setting it describes
 * We don't really do the `#  #` style commenting-out of whole sections if we can help it
 * rename `tracer_enabled` to `enabled`

While we're here, do more config parsing upfront, which makes it easier to use
later on.

Also removes redundant code from LogContextScopeManager.

Also changes the changelog fragment to a `feature` - it's exciting!

1 files changed, 2 insertions, 0 deletions

diff --git a/changelog.d/5712.feature b/changelog.d/5712.feature
new file mode 100644
index 0000000000..7d3459129d
--- /dev/null
+++ b/changelog.d/5712.feature
@@ -0,0 +1,2 @@
+Add support for opentracing.
+