Make Spacewalk benchmarks run successfully for Pendulum runtimes

[bogdanS98]

Context

Currently there are a few minor issues that prevent Spacewalk pallets benchmarks from being executed successfully on Pendulum, Amplitude and Foucoco runtimes:

• WeightInfo trait is not publicly exported for stellar-relay pallet.
• Existential deposit of native currency on all Pendulum runtimes is greater than the amount used for deposit in most Spacewalk pallets, therefore benchmarks are failing with ExistentialDeposit error here.
• vault_registry pallet uses test wrapped currencies in benchmarks and this results in failure when they are executed on any Pendulum runtime, because pairs specified in the genesis configs are different.

Requirement

Provide fixes for all of the above and re-run all benchmarks on Spacewalk.