docs: add troubleshooting page (meltano#6706)

* Add troubleshooting page

* Apply suggestions from code review

Co-authored-by: Taylor A. Murphy <taylor@meltano.com>

* Remove images in troubleshooting docs directory

Co-authored-by: Taylor A. Murphy <taylor@meltano.com>

docs/src/_guide/troubleshooting.md

@@ -0,0 +1,89 @@
+---
+title: Troubleshooting
+description: Learn what you can do if you need to troubleshoot
+layout: doc
+weight: 25
+---
+
+If you have a question about Meltano, are having trouble getting it to work, or have any kind of feedback, you can:
+
+<div class="columns is-multiline is-centered">
+    <div class="column is-half">
+      <div class="card chiclet">
+        <div class="card-content has-text-centered">
+          <div class="block">
+            <p><span class="icon is-large"><i class="fab fa-github fa-5x"></i></span></p>
+            <p>Check out the <a href="https://github.com/meltano/meltano/issues/">Meltano issue tracker</a> to see if someone else has already reported the same issue or made the same request. Feel free to weigh in with extra information, or just to make sure the issue gets the attention it deserves.</p>
+          </div>
+        </div>
+      </div>
+    </div>
+    <div class="column is-half">
+      <div class="card chiclet">
+        <div class="card-content has-text-centered">
+          <div class="block">
+            <p><span class="icon is-large"><i class="fab fa-slack fa-5x"></i></span></p>
+            <p>Join the <a href="https://meltano.com/slack">Meltano Slack workspace</a>, which is frequented by the core team and thousands of community members and data experts. You can ask any questions you may have in here or just chat with fellow users.</p>
+          </div>
+        </div>
+      </div>
+    </div>
+</div>
+
+# Common Troubleshooting Issues
+
+## Log Level Debug
+
+When you are trying to troubleshoot an issue the Meltano logs should be your first port of call.
+
+If you have a failure using Meltano's execution commands (`invoke`, `elt`, `run`, or `test`) or you're experienced general unexpected behavior, you can learn more about what’s happening behind the scenes by setting Meltano’s [`cli.log_level` setting](/reference/settings#clilog_level) to debug, using the `MELTANO_CLI_LOG_LEVEL` environment variable or the `--log-level` CLI option:
+
+```bash
+export MELTANO_CLI_LOG_LEVEL=debug
+
+meltano --log-level=debug <command> ...
+```
+
+In debug mode, Meltano will log additional information about the environment and arguments used to invoke your components (Singer taps and targets, dbt, Airflow, etc.), including the paths to the generated config, catalog, state files, etc. for you to review.
+
+Here is an example with `meltano elt`:
+
+```
+$ meltano --log-level=debug elt tap-gitlab target-jsonl --state-id=gitlab-to-jsonl
+meltano            | INFO Running extract & load...
+meltano            | INFO Found state from 2020-08-05 21:30:20.487312.
+meltano            | DEBUG Invoking: ['demo-project/.meltano/extractors/tap-gitlab/venv/bin/tap-gitlab', '--config', 'demo-project/.meltano/run/tap-gitlab/tap.config.json', '--state', 'demo-project/.meltano/run/tap-gitlab/state.json']
+meltano            | DEBUG Env: {'TAP_GITLAB_API_URL': 'https://gitlab.com', 'GITLAB_API_TOKEN': '', 'GITLAB_API_GROUPS': '', 'GITLAB_API_PROJECTS': 'meltano/meltano', 'GITLAB_API_ULTIMATE_LICENSE': 'False', 'GITLAB_API_START_DATE': '2021-03-01'}
+meltano            | DEBUG Invoking: ['demo-project/.meltano/loaders/target-jsonl/venv/bin/target-jsonl', '--config', 'demo-project/.meltano/run/target-jsonl/target.config.json']
+meltano            | DEBUG Env: {'MELTANO_EXTRACTOR_NAME': 'tap-gitlab', 'MELTANO_EXTRACTOR_NAMESPACE': 'tap_gitlab', 'MELTANO_EXTRACT_API_URL': 'https://gitlab.com', 'MELTANO_EXTRACT_PRIVATE_TOKEN': '', 'MELTANO_EXTRACT_GROUPS': '', 'MELTANO_EXTRACT_PROJECTS': 'meltano/meltano', 'MELTANO_EXTRACT_ULTIMATE_LICENSE': 'False', 'MELTANO_EXTRACT_START_DATE': '2021-03-01', 'TAP_GITLAB_API_URL': 'https://gitlab.com', 'GITLAB_API_TOKEN': '', 'GITLAB_API_GROUPS': '', 'GITLAB_API_PROJECTS': 'meltano/meltano', 'GITLAB_API_ULTIMATE_LICENSE': 'False', 'GITLAB_API_START_DATE': '2021-03-01', 'TARGET_JSONL_DESTINATION_PATH': 'output', 'TARGET_JSONL_DO_TIMESTAMP_FILE': 'False'}
+```
+
+## Dump Files Generated by Running Meltano Commands to STDOUT
+
+The [`--dump` flag](/reference/command-line-interface#parameters-1) can be passed to the `meltano invoke` and `meltano elt` commands to dump the content of a pipeline-specific generated file to `STDOUT` instead of actually running the pipeline. Note that adding support for `meltano run` is tracked in [this GitHub issue](https://github.com/meltano/meltano/issues/3072).
+
+This can aid in debugging extractor catalog generation, incremental replication state lookup, and pipeline environment variables.
+
+Supported values are:
+
+- **catalog**: Dump the extractor catalog file that would be passed to the tap’s executable using the `--catalog` option.
+- **state**: Dump the extractor state file that would be passed to the tap’s executable using the `--state` option.
+- **extractor-config**: Dump the extractor config file that would be passed to the tap’s executable using the `--config` option.
+- **loader-config**: Dump the loader config file that would be passed to the target’s executable using the `--config` option.
+
+Like any standard output, the dumped content can be redirected to a file using >, e.g. `meltano elt ... --dump=state > state.json`.
+
+Examples #
+```bash
+meltano elt tap-gitlab target-postgres --transform=run --state-id=gitlab-to-postgres
+
+meltano elt tap-gitlab target-postgres --state-id=gitlab-to-postgres --full-refresh
+
+meltano elt tap-gitlab target-postgres --catalog extract/tap-gitlab.catalog.json
+meltano elt tap-gitlab target-postgres --state extract/tap-gitlab.state.json
+
+meltano elt tap-gitlab target-postgres --select commits
+meltano elt tap-gitlab target-postgres --exclude project_members
+
+meltano elt tap-gitlab target-postgres --state-id=gitlab-to-postgres --dump=state > extract/tap-gitlab.state.json
+```