[SR-146] Updates to solution meta message

[reimerix]

This PR changes the solution meta message according to @switanis inputs:

• Remove the n_sats field
• Remove alignment_status field (the plan is to start using some bits of MSG_INS_STATUS for this in the future)
• Add tow field
• Replace TOW of last used GNSS pos/velocity fields with an age_gnss field.

[denniszollo]

LGTM. I prefer that we squash down to two commits, one with change to yaml, one with the generated files.

[GuillaumeDec]

LGTM! 🎉

[dgburr]

Which starling release will this changed message be introduced in?

[dgburr]

The TOW field is needed to be able to match information from the fusion stream with information from the PVT stream (e.g. PL values).

[reimerix]

Which starling release will this changed message be introduced in?

@dgburr We're targeting a release with the general 1.2 release slated for the end of this week.

[dgburr]

Is the new 'tow' field guaranteed to have a corresponding epoch in the PVT stream? Or is this possible:

SBP_MSG_GPS_TIME_GNSS with tow = 999 (due to ublox rounding)
SBP_SOLN_META with tow = 1000

[switanis]

I hope SOLN META TOW is the same as TOW in all other messages in the BEST POS group.
xxx_GNSS may have different TOW.