refactor: Ensure that HTTP response body objects are always closed.

[SahibYar]

This PR fixes a potential resource leak issue in our code. Previously, the HTTP response body was being ignored in cases like:

_, err := c.PostForm("/sudo", i, nil)

This oversight could lead to resource exhaustion over time. (Reference)

Changes:

•	Explicitly added resp.Body.Close() in all relevant places where HTTP requests are made.
•	Ensures that resources are properly released after the response is handled.

Testing

I ran make all and this is my output after these changes

go-fastly % make all
==> Downloading Go module
==> Downloading development dependencies
Warning: semgrep 1.104.0 is already installed and up-to-date.
To reinstall 1.104.0, run:
	brew reinstall semgrep
==> Tidying module
==> Running gofmt
==> Fixing imports
==> Testing go-fastly
?       github.com/fastly/go-fastly/v9/fastly/domains   [no test files]
?       github.com/fastly/go-fastly/v9/fastly/products  [no test files]
?       github.com/fastly/go-fastly/v9/internal/test_utils      [no test files]
ok      github.com/fastly/go-fastly/v9/fastly   2.628s
ok      github.com/fastly/go-fastly/v9/fastly/computeacls       (cached)
ok      github.com/fastly/go-fastly/v9/fastly/domains/v1        (cached)
ok      github.com/fastly/go-fastly/v9/fastly/imageoptimizerdefaultsettings     (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/botmanagement    (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/brotlicompression        (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/ddosprotection   (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/domaininspector  (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/fanout   (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/imageoptimizer   (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/logexplorerinsights      (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/ngwaf    (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/origininspector  (cached)
ok      github.com/fastly/go-fastly/v9/fastly/products/websockets       (cached)
ok      github.com/fastly/go-fastly/v9/internal/productcore     (cached)
==> Running go vet
==> Running staticcheck
staticcheck 2023.1.7 (v0.4.7)
if command -v semgrep &> /dev/null; then semgrep ci --config auto --exclude-rule generic.secrets.security.detected-private-key.detected-private-key ; fi
					
					
┌────────────────┐
│ Debugging Info │
└────────────────┘
					
	SCAN ENVIRONMENT
	versions    - semgrep 1.104.0 on python 3.13.1                       
	environment - running in environment git, triggering event is unknown
																														
	Scanning 1282 files (only git-tracked) with 1057 Code rules:
			
	CODE RULES
																														
	Language      Rules   Files          Origin      Rules                                                                
	─────────────────────────────        ───────────────────                                                               
	<multilang>      47    1162          Community    1057                                                                
	yaml             31     988                                                                                           
	go               83     153                                                                                           
	bash              4       5                                                                                           
																														
					
	SUPPLY CHAIN RULES
					
	No rules to run.
					
			
	PROGRESS
	
	━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 0:00:00                                                                                                                        
				
				
┌──────────────┐
│ Scan Summary │
└──────────────┘
Some files were skipped or only partially analyzed.
	Scan was limited to files tracked by git.
	Partially scanned: 1 files only partially analyzed due to parsing or internal Semgrep errors
	Scan skipped: 1 files larger than 1.0 MB, 119 files matching .semgrepignore patterns
	For a full list of skipped files, run semgrep with the --verbose flag.

(need more rules? `semgrep login` for additional free Semgrep Registry rules)

CI scan completed successfully.
	Found 0 findings (0 blocking) from 1057 rules.
	No blocking findings so exiting with code 0

[Integralist]

@philippschulte this might be worth including in a patch release.

[kpfleming]

Thanks for this contribution! I'm not thrilled about having to repeat this code pattern all over the place, as it will likely lead to a future programmer forgetting to do it, but I can't think of a practical way to avoid the duplication.