Fix #297, base offsets for CF msgids

[jphickey]

Checklist (Please check before submitting)

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Describe the contribution
Define the CF msgids as an offset from the CFE_PLATFORM_CMD_MID_BASE or CFE_PLATFORM_TLM_MID_BASE, which helps simplify configuration.

Users should add MSG offsets to the global mission config header.

Fixes #297

Testing performed
Build and run CF app

Expected behavior changes
MsgIds for CF can be more easily customized by setting MSG offsets in the global cfe_mission_cfg.h header file, the same way other CFE framework module msgids are set. User does not need to modify this file in place to do so.

System(s) tested on
Ubuntu 22.04

Contributor Info - All information REQUIRED for consideration of pull request
Joseph Hickey, Vantage Systems, Inc.

[skliper]

Not quite convinced a change in one file in one app is appropriate/sufficient to address the general problem of platform/mission configuration overrides. II guess it fixes the stated issue but I'm not a huge fan of the one-off nature. Could just use the generate_config_includefile to solve the immediate problem (and implement across all actively maintained apps) and address the transition to topic ids as a more thorough/future change.

If we do accept this concept, maybe XXX_MID_OFFSET, or XXX_TID (Topic ID?) or OMID (Offset MID)? I do like eventually switching to the topic concept and not need to recompile a the app just for a MID change, so I'm in favor of using names that lead us down that path if we are going to make updates like this.

[skliper]

Side note, whichever way we go I think we should still provide the override capability for whichever direction we choose. There's enough different MID management schemes that I don't think forcing one approach is the best fit. Within some toolchains it may be easier to have one full MID list and mask them to get the topic or whatever (just making up use cases...) Which I guess is still possible here but adds layers of abstraction when just one or two would be enough, and we don't need to require users to use this file.

[jphickey]

Yeah I fully concur that this is not a real complete solution at all - its just a baby step, in one app. But this is the way that CFE itself does it, and IMO its easier to manage because offsets can be defined globally.

With the way this is done, its still evaluated at compile time, not run time - so changing a MID still requires rebuilding the app. I'd definitely prefer a solution where the MID determination was done more at runtime than compile time to avoid having to rebuild apps to update this stuff, but this PR doesn't do that.

I'm perfectly fine if this is deferred/not merged, I can just patch my own build in the meantime - but the problem is that every user of CF likely has to also patch their build too, and its not the easiest thing to manage in a deployment.

[dzbaker]

CCB 3 Aug 2022: Deferring for now.

[skliper]

CCB:20220802 - Deferring this as a point fix in preference for more global fixes to header file customization and topic ids.

[skliper]

In theory you can just override as documented in nasa/cFS#403.

[jphickey]

Superseded by #423