feat: improve token generation commands

[sweatybridge]

What kind of change does this PR introduce?

feature

What is the new behavior?

Bearer JWT

• Supports --payload flag for custom claims like {"aud":"test"}
• Computes issued at timestamp based on expiry date
• Stop generating legacy jwt keys to discourage using it
• Prompt to choose signing key when generating bearer jwt

Signing Key

• Only print a single key to stdout (instead of a prettified array)
• Supports piping commands, ie. supabase gen signing-key | supabase gen bearer-jwt
• Drops the uuid requirement on kid so it's more general

Additional context

Add any other context or screenshots.

[coveralls]

Pull Request Test Coverage Report for Build 18126126581

Details

• 31 of 123 (25.2%) changed or added relevant lines in 3 files are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.1%) to 54.78%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/gen/bearerjwt/bearerjwt.go	29	47	61.7%
cmd/gen.go	0	32	0.0%
internal/gen/signingkeys/signingkeys.go	2	44	4.55%

Files with Coverage Reduction	New Missed Lines	%
internal/gen/signingkeys/signingkeys.go	1	43.97%
internal/gen/keys/keys.go	5	12.9%

Totals
Change from base Build 18098239643:	-0.1%
Covered Lines:	6389
Relevant Lines:	11663

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💛 - Coveralls