feat: Add nf-conda package manager plugin

Creates the nf-conda plugin that implements conda support for the
unified package management system:

- CondaPlugin: Main plugin class
- CondaPackageProvider: Implements PackageProvider interface
- CondaProviderExtension: Registers the provider with Nextflow
- Includes existing CondaCache and CondaConfig implementations

This plugin enables conda package management through the new
unified 'package' directive while maintaining all existing
conda functionality and configuration options.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>
Signed-off-by: Edmund Miller <[email protected]>

Author: edmundmiller

plugins/nf-conda/build.gradle

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2021-2023, Seqera Labs
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+plugins {
+    id 'nextflow-plugin'
+}
+
+group = 'io.nextflow'
+version = '1.0.0'
+gitBranch = 'main'
+
+dependencies {
+    // plugin dependencies
+    api project(':nextflow')
+    
+    // test dependencies
+    testImplementation(testFixtures(project(':nextflow')))
+    testImplementation 'org.codehaus.groovy:groovy-test:3.0.19'
+    testImplementation 'org.spockframework:spock-core:2.3-groovy-3.0'
+    testImplementation 'org.testcontainers:testcontainers:1.20.0'
+    testImplementation 'org.testcontainers:spock:1.20.0'
+}