fix: show customer name for naming series in process soa

[GursheenK]

Problem

• In Process Statement of Accounts - GL and AR the default subject and body of the email used the name field for specifying the customer. However, in cases where the name of the Customer document is different from the customer_name field (eg: when naming series is used for Customer doctype), the subject and body of the email show the document name instead of the customer name.
• For the AR report, the html template fetches the name field instead of the customer_name.
• AR report PDF does not show the Letterhead and Terms.

Solution

• Used customer_name field instead of name wherever necessary.
• Added HTML code for rendering Letterhead and Terms in AR Report.

Notes for Reviewer

As mentioned in the issue, there was a need to use the Subject as the PDF name before sending the report PDF in the email. Have added an extra field for specifying the PDF name format in Email Settings to keep things general. Please mention if a different approach can be used here.

no-docs

[codecov]

Codecov Report

Merging #36843 (060da2c) into develop (91927f2) will increase coverage by 0.21%.
Report is 31 commits behind head on develop.
The diff coverage is 77.77%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #36843      +/-   ##
===========================================
+ Coverage    65.39%   65.61%   +0.21%     
===========================================
  Files          794      794              
  Lines        62122    62189      +67     
===========================================
+ Hits         40626    40805     +179     
+ Misses       21496    21384     -112     

Files Changed	Coverage Δ
...ement_of_accounts/process_statement_of_accounts.py	58.85% <77.77%> (+58.85%)	⬆️

... and 14 files with indirect coverage changes