Prepare release v0.77.0 (#3139)

Update changelog for v0.77.0 release of the Splunk OpenTelemetry
collector.

CHANGELOG.md

@@ -2,6 +2,18 @@
 
 ## Unreleased
 
+## v0.77.0
+
+This Splunk OpenTelemetry Collector release includes changes from the [opentelemetry-collector v0.77.0](https://github.com/open-telemetry/opentelemetry-collector/releases/tag/v0.77.0) and the [opentelemetry-collector-contrib v0.77.0](https://github.com/open-telemetry/opentelemetry-collector-contrib/releases/tag/v0.77.0) releases where appropriate.
+
+### 💡 Enhancements 💡
+
+- `connector/forward` - Add support for the forward connector ([#3100](https://github.com/signalfx/splunk-otel-collector/pull/3100))
+- `receiver/signalfxgatewayprometheusremotewritereceiver` - Add new receiver that aims to be an otel-native version of
+  the SignalFx [Prometheus remote write](https://github.com/signalfx/gateway/blob/main/protocol/prometheus/prometheuslistener.go)
+  [gateway](https://github.com/signalfx/gateway/blob/main/README.md) ([#3064](https://github.com/signalfx/splunk-otel-collector/pull/3064))
+- `signalfx-agent`: Relocate to be internal to the collector ([#3052](https://github.com/signalfx/splunk-otel-collector/pull/3052))
+
 ## v0.76.1
 
 ### 💡 Enhancements 💡