Feat: Allow param filename configuration per target with the CFn prov…

…ider + bugfixes (#565)

* Fix ADF Codepipeline readability and line length

* Refactor CodePipeline target, fallback default config retrieval

* Feat: Allow param filename configuration per target with the CFn provider

**Why?**

Allowing a specific parameter file to be used. This is especially useful if you
would like to reuse a template. Often these templates are committed or generated
with another generator than generate_params.py.

**What?**

* Added params_filename to the CloudFormation provider schema.
* Updated the CloudFormation provider to support setting the params_filename.
* Documented the param_filename property in the CloudFormation provider docs.

* Improve doc on CodeBuild Role usage in the deploy account

* Refactor contains transform template name logic CFn provider

docs/providers-guide.md

@@ -284,6 +284,9 @@ Provider type: `codebuild`.
     pipeline. Alternatively, you can change the `adf-codebuild-role` with
     additional permissions and conditions in the `global-iam.yml` file as
     documented in the [User Guide](./user-guide.md).
+    **Please note:** Since the CodeBuild environment runs in the deployment
+    account, the role you specify will be assumed in and should be available
+    in the deployment account too.
 - *timeout* *(Number)* in minutes, default: `20`.
   - If you wish to define a custom timeout for the Build stage.
 - *privileged* *(Boolean)* default: `False`.
@@ -553,6 +556,16 @@ Provider type: `cloudformation`.
     file name to use allows you to generate multiple templates, where a specific
     template is used according to its specific target environment. For example:
     `template_prod.yml` for production stages.
+- *param_filename* - *(String)* default: `${target_account_name}_${target_region}.yml`.
+  - The name of the CloudFormation Parameter file to use. Changing the
+    parameter file name to use allows you to generate a single parameter file
+    that is shared between many when required.
+    The parameter file is read from inside the `${root_dir}/params/` folder.
+    **Please note:** Setting this parameter will **not** change the behavior
+    of the generate_params.py script. It is recommended to copy the generated
+    template that you would like to reuse after running generate_params.py
+    and use the name of the copied file as the configuration here when
+    required.
 - *root_dir* - *(String)* default to empty string.
   - The root directory in which the CloudFormation template and `params`
     directory reside. Example, when the CloudFormation template is stored in