[ROS2] reconfigurable transport scoped parameters for theora

[bmegli]

140 fix for theora_image_transport (publisher and subscriber)

108 like (runtime reconfigurable)

Implementation is #143 like + minor deviation for publisher.

The original logic behind dynamic reconfigure callbacks was kept.

publisher notes

The publisher is more complex here

• in general we reload config on publish
• but some code paths (conditional compilation)
  • would result in resetting theora context on every config reload
  • so we flag to reload config only on parameter event change
    • and reload it also once on init to mimic ROS1 dynamic reconfigure setup

This is different from all other transport scoped changes so far where we could make transport reconfigurable without depending on parameter event monitoring (in the spirit of #108).

The difference is only in setting/resetting/checking flag but event handling code exists only for the purpose of deprecated parameters in other transports.

code repetition

There is some code repetition between:

• compressed_image_transport
• compressed_depth_image_transport
• theora_image_transport

This should be temporary until deprecated parameters are removed.

The way to proceed was sketched in:

• https://github.com/ros-perception/image_transport_plugins/issues/140#issuecomment-1525806469

[bmegli]

Should be fixed now.

The only deviation was in subscriber which has parameter post_processing_level, the comments where based on it.

[ijnek]

@Mergifyio backport iron

[mergify[bot]]

backport iron

✅ Backports have been created

* [#147 [ROS2] reconfigurable transport scoped parameters for theora (backport #146)](https://github.com/ros-perception/image_transport_plugins/pull/147) has been created for branch `iron`