config: allow spreading config over multiple files

This is the Go-equivalent to

This commit enables spreading the config in /etc/sr.ht - and, crucially,
_only_ in /etc/sr.ht - over multiple .ini files.

If a file config.ini is found (either in current or parent directory, or
/etc/sr.ht) it (and only it) is loaded and any other ini files are
ignored. To utilize multiple configs, they must be in /etc/sr.ht, and
none of them must be called config.ini.

Spreading the config over multiple files will make it much easier to
create containerized versions, where e.g. different secrets can be made
available in different files, but rendering it all into one big file
would require some preprocessing.
auth: add auth.IPAddress

With support for X-Forwarded-For
auth/middleware: set WWW-Authenticate header field

See RFC 6750 section 3.
s3: add Enabled
client: rename Execute to Do

583d0b1bcb08 ("client/graphql: handle GraphQL errors") changed
Execute behavior by wrapping the result into a struct with "data"
and "errors" fields. This is a breaking change, but it's hard to
spot when upgrading core-go because it won't cause a compilation

Rename Execute to Do to break the build and force callers to update
auth: add RequireMiddleware

Same as Middleware, but requires auth for all requests. Will be
useful to drop hacks from pages.sr.ht.
s3: add [objects]s3-insecure

Disables TLS. Useful for local development.
s3: add NewClient and URL

Centralizes the logic to create an S3 client and get the base URL.
email: make PGP private key optional

Services other than meta.sr.ht don't really have a use for the
private PGP key.

Add a CanPGPSign method so that meta.sr.ht can emit a warning or
error when the PGP key is missing.
client/graphql: handle GraphQL errors

Instead of leaving it up to the caller to check for GraphQL errors,
centralize in core-go.
email: improve mail.ParseAddress error message
server/directives: disambiguate AnonInternal error message

AUTH_INTERNAL won't work with AnonInternal.
Drop gqlparser v1 dependency

Only use v2 throughout the repository.
Update and simplify build manifest

Alpine 3.14 uses Go 1.16, but go.mod says 1.17. Also, no external
repository should be required for core-go.
webhooks: skip webhooks with expired credentials

The documentation states [1]:

> When the original authentication method becomes invalid (such as the
> expiration of or revocation of an OAuth 2.0 bearer token), the
> webhook is disabled.

However, this is currently not the case. Expired webhooks are indeed
filtered out in virtually all GraphQL queries (by means of core-go's
FilterWebhooks [2]), so users cannot see or delete them. They are _not_
filtered out upon scheduling, however. This commit fixes that.

The symptoms of this are that active webhooks may simply not be run - if
a user has both an expired and a valid, active webhook for some event,
the scheduling will retrieve both, fail on the expired one, and stop
processing, without any feedback to the user who scheduled the hooks.

This is a problem across all services, so core-go seems like the best
place to fix this.

[1]: https://man.sr.ht/graphql.md#webhook-authentication
[2]: https://git.sr.ht/~sircmpwn/core-go/tree/master/item/webhooks/config.go#L74,81
Migrate to chi v5

v1 is not maintained anymore.
database: don't panic on context.DeadlineExceeded

Checking context.Cancelled is not enough, I also see the same issue
with context.DeadlineExceeded:

    panic: Transaction error: driver: bad connection
    Closure error: context deadline exceeded

    goroutine 66664 [running]:
    git.sr.ht/~sircmpwn/core-go/database.WithTx({0x5578e1847a58, 0xc0002c44e0}, 0x50?, 0xc000285f38)
            e7b8e02696a1">git.sr.ht/~sircmpwn/core-go@v0.0.0-20231129165057-e7b8e02696a1/database/middleware.go:74 +0x2ce
    git.sr.ht/~sircmpwn/builds.sr.ht/api/loaders.fetchUsersByID.func1({0xc0002cf190, 0x1, 0x1})
            git.sr.ht/~sircmpwn/builds.sr.ht/api/loaders/middleware.go:34 +0x118
    git.sr.ht/~sircmpwn/builds.sr.ht/api/loaders.(*usersByIDLoaderBatch).startTimer(0xc00044a360, 0xc00042d380)
            git.sr.ht/~sircmpwn/builds.sr.ht/api/loaders/usersbyidloader_gen.go:218 +0xe7
    created by git.sr.ht/~sircmpwn/builds.sr.ht/api/loaders.(*usersByIDLoaderBatch).keyIndex
            git.sr.ht/~sircmpwn/builds.sr.ht/api/loaders/usersbyidloader_gen.go:191 +0x119
server/email: use go-message for address parsing

No need to additionally depend on net/mail
database: print both errors in WithTx

Make it easier to debug panics by printing both errors instead of
sending one of them to /dev/null.
database/middleware: fix error value used in panic

We were checking txErr, but panic'ing with err.

Fixes: a06a6247898c ("database: don't panic with ErrBadConn")