[Feature] Make sentry optional

[Grvzard]

If we make sentry an optional feature, the number of dependencies in pingora-core will decrease by around 70+. And it will significantly reduce the size of the binary.

[eaufavor]

working on this right now

[moderation]

I'm getting a build error on main after the Sentry option PR https://github.com/cloudflare/pingora/pull/410

env RUST_BACKTRACE=full RUST_LOG=INFO mold --run cargo run --example test --release --no-default-features --features=boringssl
   Compiling pingora-core v0.3.0 (~/Library/rust/pingora/pingora-core)
error[E0433]: failed to resolve: use of undeclared crate or module `sentry`
   --> pingora-core/src/server/mod.rs:122:29
    |
122 | ...                   sentry::capture_error(&e);
    |                       ^^^^^^ use of undeclared crate or module `sentry`

error[E0609]: no field `sentry` on type `&mut Server`
   --> pingora-core/src/server/mod.rs:264:27
    |
264 |         let _guard = self.sentry.as_ref().map(|opts| sentry::init(opts.clone()));
    |                           ^^^^^^ unknown field
    |
    = note: available fields are: `services`, `listen_fds`, `shutdown_watch`, `shutdown_recv`, `configuration`, `options`

error[E0433]: failed to resolve: use of undeclared crate or module `sentry`
   --> pingora-core/src/server/mod.rs:264:54
    |
264 |         let _guard = self.sentry.as_ref().map(|opts| sentry::init(opts.clone()));
    |                                                      ^^^^^^ use of undeclared crate or module `sentry`

error[E0433]: failed to resolve: use of undeclared crate or module `sentry`
   --> pingora-core/src/server/mod.rs:279:17
    |
279 |                 sentry::capture_error(&e);
    |                 ^^^^^^ use of undeclared crate or module `sentry`

error[E0609]: no field `sentry` on type `Server`
   --> pingora-core/src/server/mod.rs:308:27
    |
308 |         let _guard = self.sentry.as_ref().map(|opts| sentry::init(opts.clone()));
    |                           ^^^^^^ unknown field
    |
    = note: available fields are: `services`, `listen_fds`, `shutdown_watch`, `shutdown_recv`, `configuration`, `options`

error[E0433]: failed to resolve: use of undeclared crate or module `sentry`
   --> pingora-core/src/server/mod.rs:308:54
    |
308 |         let _guard = self.sentry.as_ref().map(|opts| sentry::init(opts.clone()));
    |                                                      ^^^^^^ use of undeclared crate or module `sentry`

Some errors have detailed explanations: E0433, E0609.
For more information about an error, try `rustc --explain E0433`.
error: could not compile `pingora-core` (lib) due to 6 previous errors

[Grvzard]

I'm getting a build error on main after the Sentry option PR https://github.com/cloudflare/pingora/pull/410

https://github.com/cloudflare/pingora/pull/399#issuecomment-2398927180