Add bastion feeder support

[AlCutter]

This PR configures the newly added bastion feeder in the armored witness.

Tested locally on AW hardware (with an Applet built using a patched feeder to add InsecureSkipVerify: true); feedbastion -> local litebastion instance -> AW via bastion_feeder:

❯ go run ./cmd/feedbastion --bastion_url=https://localhost:8443/3a8a5615f38f0e3388d389d031353a6041acd12b30b38d5b6ddcaf16fd01dcc1/add
I0612 17:07:22.746601  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0pDHaWYAAAAA0emjnVBR5V7ZypPaXdB6r0A7d44kLC4a/2Q6WMpjrzOZg3Tizif+rgcxdKKJ0rNLEvwz1jYoUx7WRorLboNEDQ==
I0612 17:07:22.895499  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0k64aWYAAAAAIFemKhHzezp04HUQquRLjsaMxewIte/R+H0Rl7FNUEd+kCkAu8oYVwfSdGum9fJgkXKnkksXH95UNUDMZpQlAQ==
I0612 17:07:23.112839  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0lK4aWYAAAAAOtRh8zip27HyalmfxEMYIEKDpNrRC2ztA0kyOBpcRiPqk5fEQD3J4lF62yz/lbYnz+IjXYKdhBUjcpnCtQFWCw==
I0612 17:07:23.192449  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0ku4aWYAAAAAAUcqM1gXtsbCA9B1P/yQtmSu7ApBlD40YvvIinHgEd8jaFJYHuhM4RWGkW6Ty9iYhFAnVtvHvym/msynagRmDQ==
I0612 17:07:23.334780  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0ka4aWYAAAAAQzdvVCb415vkzbukLUH1pz5V8jgaN/gqQwNHahlaudw41aUhV+tdFVgNhM5Lof3LbPHrj4QBZmT5OScPkgW3CA==
I0612 17:07:23.602979  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0lS4aWYAAAAAmQVJ9yMMBm37DMnIYC1FTo/XH/bJCoF80eaXNwmJpM8v/Esr19s1qyoy3cnsNmhqXTKaUTHCvLtzOISxKdSGDQ==
I0612 17:07:23.955488  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0t7GaWYAAAAAaWT3m61b+Cl1eT1jFuxKMlb8wYJHLZqzMvfxz6HLOguei/SKMAId7OVjFrUSo+oIg3vMzv32od0Qxe5+Qe2wDA==
I0612 17:07:24.380595  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0le4aWYAAAAAcKbfOuakPcNtVLo/6kC00zVkMZll0DfQPzVsapM7ZFmhk8zhksjuyfs8+UwUFPqGxGM5XzID1TE7W5m2B/RGCQ==
I0612 17:07:24.920853  124885 main.go:131] 200 OK:
— DEV:ArmoredWitness-misty-snow TrDK0km4aWYAAAAAVukugQGbIabDuiN/odGDpA8moypvzMvmWcho9I9PsZiES/gUtOnypq8SqDWmuMwmtyPDAXbRnuLhuBUuU7FuCA==

Towards transparency-dev/armored-witness#253