Setup Default 7.x Branch (#688)

Add 7.x branch designations to GitHub workflow configurations and README.md.

Author: jasonhebert

.github/workflows/automation-changelog-update.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - "6.x"
+      - "7.x"
 
 jobs:
   automation:

.github/workflows/docs.yml

@@ -5,6 +5,7 @@ on:
   push:
     branches:
       - "6.x"
+      - "7.x"
 
 jobs:
   documentation-linter:

.github/workflows/test-suite.yml

@@ -5,6 +5,7 @@ on:
   push:
     branches:
       - "6.x"
+      - "7.x"
   schedule:
     - cron:  '0 8 * * *'
 

README.md

@@ -63,6 +63,7 @@ This library is not in a stable stage yet, please use with caution.
 | [4.x](https://github.com/amazon-php/sp-api-sdk/tree/4.x) | 🚫         |
 | [5.x](https://github.com/amazon-php/sp-api-sdk/tree/5.x) | 🚫         |
 | [6.x](https://github.com/amazon-php/sp-api-sdk/tree/6.x) | ✅         |
+| [7.x](https://github.com/amazon-php/sp-api-sdk/tree/7.x) | ✅         |
 
 Version <s> [1.x](https://github.com/amazon-php/sp-api-sdk/tree/1.x) </s> is deprecated becuase of the attempt to
 make a little more sense of what Amazon is doing with using "tags" in their Open API specification.