pipelines: add generate command (#4251)

## Changes
Add `databricks pipelines generate` command that generates DAB resources
from SDP YAML.

`generate` command is tailored to `lakeflow-pipelines` template where
`src` folder contains pipeline folders, for example:

```
├── databricks.yml
├── pyproject.toml
├── README.md
├── resources
│   ├── my_pipeline.pipeline.yml
│   └── my_pipeline.job.yml
└── src
    └── my_pipeline
        ├── spark-pipeline.yml
        └── transformations
            ├── example_python_materialized_view.py
            └── example_sql_materialized_view.sql
```

### Usage

```
$ databricks pipelines generate src/my_pipeline
```

Where `src/my_pipeline/sdp-pipeline.yml`:

```yaml
name: My Pipeline
storage: file:///Users/foo/bar/baz
libraries:
  - glob:
      include: transformations/**
```

Produces `resources/my_pipeline.pipeline.yml`:

```yaml
resources:
  pipelines:
    my_pipeline:
      name: My Pipeline
      catalog: ${var.catalog}
      schema: ${var.schema}
      root_path: ../src/my_pipeline
      serverless: true
      libraries:
        - glob:
            include: ../src/my_pipeline/transformations/**
      environment:
        dependencies:
          - --editable ${workspace.file_path}
```

## Why
It allows creating DAB YAML for Spark Declarative Pipelines

## Tests
Acceptance and unit tests

Author: kanterov

acceptance/pipelines/databricks-cli-help/output.txt

@@ -22,6 +22,7 @@ Available Commands
   deploy                Deploy pipelines
   destroy               Destroy a pipelines project
   dry-run               Validate correctness of the pipeline's graph
+  generate              Generate pipeline configuration
   history               Retrieve past runs for a pipeline
   init                  Initialize a new pipelines project
   logs                  Retrieve events for a pipeline

acceptance/pipelines/generate/bad-path/out.test.toml

@@ -0,0 +1,5 @@
+
+>>> errcode [CLI] pipelines generate --existing-pipeline-dir /tmp/foo
+Error: please make sure the directory is located in side 'src/' (for example 'src/my_pipeline'), got: [path]
+
+Exit code: 1

acceptance/pipelines/generate/bad-path/output.txt

@@ -0,0 +1,3 @@
+export ENABLE_PIPELINES_CLI=1
+
+trace errcode $CLI pipelines generate --existing-pipeline-dir /tmp/foo

acceptance/pipelines/generate/bad-path/script

@@ -0,0 +1,5 @@
+# printed paths are different on Windows
+
+[[Repls]]
+Old = "got: .*"
+New = "got: [path]"

acceptance/pipelines/generate/bad-path/test.toml

@@ -0,0 +1,2 @@
+Generated pipeline configuration: resources/my_pipeline.pipeline.yml
+

acceptance/pipelines/generate/discover-spark-pipeline-yml/out.test.toml

@@ -0,0 +1,14 @@
+resources:
+  pipelines:
+    my_pipeline:
+      name: My Pipeline
+      catalog: ${var.catalog}
+      schema: ${var.schema}
+      root_path: ../src/my_pipeline
+      serverless: true
+      libraries:
+        - glob:
+            include: ../src/my_pipeline/transformations/**
+      environment:
+        dependencies:
+          - --editable ${workspace.file_path}

acceptance/pipelines/generate/discover-spark-pipeline-yml/output.txt

@@ -0,0 +1,5 @@
+export ENABLE_PIPELINES_CLI=1
+
+$CLI pipelines generate --existing-pipeline-dir src/my_pipeline
+
+mv resources output/

acceptance/pipelines/generate/discover-spark-pipeline-yml/output/my_pipeline.pipeline.yml

@@ -0,0 +1,5 @@
+name: My Pipeline
+storage: file:///Users/foo/bar/baz
+libraries:
+  - glob:
+      include: transformations/**