fix(federation/query-planning): Prevent error for satisfiable @shareable mutation fields

[sachindshinde]

This PR fixes a bug where query planning may unexpectedly error while planning an operation with a satisfiable @shareable mutation field.

Specifically, this PR:

1. Updates query planning on mutation fields to only consider one initial subgraph at a time for a traversal, and returns the plan with lowest cost.
   • Previously, this was mixing up options that started in different subgraphs in the same traversal, which would sometimes generate query planning errors if those differing options were chosen. There were a few ways to fix this, but the least invasive/simplest was just to do multiple traversals, each with a limited initial subgraph.
2. Updates a particular query planning optimization to avoid discarding an option if another option with less subgraph jumps/cost is found, if that option starts in a different subgraph and the option is for a mutation operation.

This PR is the equivalent of this JS repo PR.

Unrelatedly, this PR also fixes an error messaging issue when QP unexpectedly doesn't find a plan (this shouldn't happen, but if it did, it was previously using the wrong federation error enum and message).

[apollo-librarian]

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[dariuszkuc]

Corresponding JS fix

[sachindshinde]

@dariuszkuc
That PR has been split up, and this PR corresponds more closely to apollographql/federation#3304 now.

[duckki]

Looks great! The fix makes sense and I confirmed the test is now fixed.