lnd+config: add ability to obtain blocking and mutex profiles

In this commit, we add the ability to obtain blocking and mutex
profiles. The blocking profile will show which goroutines are
consistently blocked on synchronization primitives like channels, or
I/O. The mutex profile will show which mutexes are very contested.

The blocking profile can be enabled with a new arg: `--blockingprofile`.
The mutex profile can be enabled with a new arg: `--mutexprofile`. These
are both ignored if the profile port isn't set.

Activating these profiles requires the caller to pass in a sampling
rate. For now I've set it just to `1` to test things out. Unfortunately
documentation is rather scarce, so there aren't any good guides re what
these values should be set to. AFAICT, these add more overhead than the
other prowling options, so they shouldn't necessarily be enabled
persistently in production.

docs/release-notes/release-notes-0.17.0.md

@@ -77,6 +77,11 @@ fails](https://github.com/lightningnetwork/lnd/pull/7876).
 
 # New Features
 ## Functional Enhancements
+
+* `lnd` can now optionally generate [blocking and mutex
+  profiles](https://github.com/lightningnetwork/lnd/pull/7983). These profiles
+  are useful to attempt to debug high mutex contention, or deadlock scenarios.
+
 ### Protocol Features
 * This release marks the first release that includes the new [musig2-based
   taproot channel type](https://github.com/lightningnetwork/lnd/pull/7904). As