chore: clean up all markdown lint errors in root directory (#10154)

CONTRIBUTING.md

@@ -1,4 +1,4 @@
-### Contributing
+# Contributing
 
 1. [Sign the CLA][cla].
 2. Open a [new issue][] to discuss the changes you would like to make.  This is
@@ -16,30 +16,32 @@
 
 **Note:** If you have a pull request with only one commit, then that commit needs to follow the conventional commit format or the `Semantic Pull Request` check will fail. This is because github will use the pull request title if there are multiple commits, but if there is only one commit it will use it instead.
 
-#### When will your contribution get released?
+## When will your contribution get released?
+
 We have two kinds of releases: patch releases, which happen every few weeks, and feature releases, which happen once a quarter. If your fix is a bug fix, it will be released in the next patch release after it is merged to master. If your release is a new plugin or other feature, it will be released in the next quarterly release after it is merged to master. Quarterly releases are on the third Wednesday of March, June, September, and December.
 
-#### Contributing an External Plugin
+## Contributing an External Plugin
 
 Input, output, and processor plugins written for internal Telegraf can be run as externally-compiled plugins through the [Execd Input](/plugins/inputs/execd), [Execd Output](/plugins/outputs/execd), and [Execd Processor](/plugins/processors/execd) Plugins without having to change the plugin code.
 
 Follow the guidelines of how to integrate your plugin with the [Execd Go Shim](/plugins/common/shim) to easily compile it as a separate app and run it with the respective `execd` plugin.
 Check out our [guidelines](/docs/EXTERNAL_PLUGINS.md#external-plugin-guidelines) on how to build and set up your external plugins to run with `execd`.
 
-#### Security Vulnerability Reporting
+## Security Vulnerability Reporting
+
 InfluxData takes security and our users' trust very seriously. If you believe you have found a security issue in any of our
 open source projects, please responsibly disclose it by contacting security@influxdata.com. More details about
 security vulnerability reporting,
 including our GPG key, [can be found here](https://www.influxdata.com/how-to-report-security-vulnerabilities/).
 
-### GoDoc
+## GoDoc
 
 Public interfaces for inputs, outputs, processors, aggregators, metrics,
 and the accumulator can be found in the GoDoc:
 
 [![GoDoc](https://godoc.org/github.com/influxdata/telegraf?status.svg)](https://godoc.org/github.com/influxdata/telegraf)
 
-### Common development tasks
+## Common development tasks
 
 **Adding a dependency:**
 
@@ -52,7 +54,7 @@ Telegraf uses Go modules. Assuming you can already build the project, run this i
 Before opening a pull request you should run the linter checks and
 the short tests.
 
-```
+```shell
 make check
 make test
 ```
@@ -63,24 +65,27 @@ make test
 
 Running the integration tests requires several docker containers to be
 running.  You can start the containers with:
-```
+
+```shell
 docker-compose up
 ```
 
 To run only the integration tests use:
 
-```
+```shell
 make test-integration
 ```
 
 To run the full test suite use:
-```
+
+```shell
 make test-all
 ```
 
 Use `make docker-kill` to stop the containers.
 
 ### For more developer resources
+
 - [Code Style][codestyle]
 - [Deprecation][deprecation]
 - [Logging][logging]

EXTERNAL_PLUGINS.md

@@ -6,6 +6,7 @@ Check out the [external plugin documentation](/docs/EXTERNAL_PLUGINS.md) for mor
 Pull requests welcome.
 
 ## Inputs
+
 - [awsalarms](https://github.com/vipinvkmenon/awsalarms) - Simple plugin to gather/monitor alarms generated  in AWS.
 - [octoprint](https://github.com/BattleBas/octoprint-telegraf-plugin) - Gather 3d print information from the octoprint API.
 - [opcda](https://github.com/lpc921/telegraf-execd-opcda) - Gather data from [OPC Fundation's Data Access (DA)](https://opcfoundation.org/about/opc-technologies/opc-classic/) protocol for industrial automation.
@@ -27,8 +28,9 @@ Pull requests welcome.
 - [db2](https://github.com/bonitoo-io/telegraf-input-db2) - Gather the statistic data from DB2 RDBMS
 
 ## Outputs
+
 - [kinesis](https://github.com/morfien101/telegraf-output-kinesis) - Aggregation and compression of metrics to send Amazon Kinesis.
 
 ## Processors
- - [geoip](https://github.com/a-bali/telegraf-geoip) - Add GeoIP information to IP addresses.
 
+- [geoip](https://github.com/a-bali/telegraf-geoip) - Add GeoIP information to IP addresses.