PSDK core functions + subscribers + basic flight control

[biancabnd]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	(Closes #IssueNumber)
Primary OS tested on	(Ubuntu, MacOS, Windows)
Robotic platform tested on	DJI M300 HITL

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Description of contribution in a few bullet points

• Implemented core functions to create and init a DJI PSDK application
• Implemented the most important topic subscribers and brought them to ROS
• Implemented the most important flight control services (e.g. land, takeoff, control position, control velocity)

Description of documentation updates required from your changes

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• Add documentation in Confluence page

Future work that may be required in bullet points

• Add the remaining topic subscribers from DJI
• Add more checks through the entire pipeline to make sure that there is no safety concern/ bug within the PSDK library itself
• Test and spot weak points that can be improved

Review Check

• There are no conflicts with target branch.

• Description is intelligible and well written.

• Passes the CI tests.

• README.md is updated.

[vicmassy]

Stunning work @biancabnd ! Really impressive, huge amount of work put here. Overall the code looks clean, readable and well structured. I added few comments, mainly to trigger some discussions.

Congrats on this 🚀 ⭐

Being the richest man in the cemetery doesn't matter to me. Going to bed at night saying we've done something wonderful, that's what matters to me. - Steve Jobs