Added various features to flash analysis

[alexcekay]

Solved Problem

There has been feedback regarding the FLASH analysis tool. This PR adds several of the requested features.

• Use an updated version of bloaty
• Show the FLASH diff directly, without the user having to scroll through the bloaty output
• Don't show a comment for small changes
• The analysis shall also work if the FLASH overflows

Solution

• To use an updated bloaty version and return the diff to the GH action an adaption of the bloaty-action was required. These changes can be found here: https://github.com/PX4/bloaty-action
• The action itself has been updated to show the diff and not post a comment if the diff is too small.
• To avoid no ELF being created due to a FLASH overflow (and thus no option to do the analysis), a new flash-analysis board has been added to v5x and v6x which fakes a large FLASH.

Test coverage

• Has been tested on my fork of PX4 in some test pull requests
  • Change alexcekay/PX4-Autopilot#14
  • Old branch test alexcekay/PX4-Autopilot#13

[mrpollo]

Nice additions!

I left some comments, mainly focused on readability/maintainability for whoever comes after us and tries to figure this out

[niklaut]

Nice, let's get this in.