Import assets from markdown file

[Mukund-Tandon]

This PR adds support to detect images from markdown file which are in  format
It also fixes the error where if a file is there in markdown file it is detected as a url since both have a similar representation in markdown - [Alt tex](url or file path) not if it is a file it is treated as a simple paragraph with text "This is currently not supported : [Alt text](file path)"
Related to AppFlowy-IO/AppFlowy#2981

[codecov]

Codecov Report

Merging #316 (800ebba) into main (87fd7ed) will increase coverage by 3.16%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##             main     #316      +/-   ##
==========================================
+ Coverage   72.24%   75.40%   +3.16%     
==========================================
  Files         237      238       +1     
  Lines        9539     9649     +110     
==========================================
+ Hits         6891     7276     +385     
+ Misses       2648     2373     -275     

Impacted Files	Coverage Δ
...ns/markdown/decoder/document_markdown_decoder.dart	94.68% <93.33%> (-0.26%)	⬇️

... and 54 files with indirect coverage changes

[Mukund-Tandon]

@LucasXu0 ,please can you review this PR

[LucasXu0]

@LucasXu0 ,please can you review this PR

@Mukund-Tandon I did some changes.

• use regex to match the image path and file path.
• remove the hint text(... not supported...).
• define the regexes as class properties.

[Mukund-Tandon]

@LucasXu0 ,please can you review this PR

@Mukund-Tandon I did some changes.

• use regex to match the image path and file path.
• remove the hint text(... not supported...).
• define the regexes as class properties.

Ok 👍

[Mukund-Tandon]

@LucasXu0 , Is there anything else I need to do?

[LucasXu0]

@LucasXu0 , Is there anything else I need to do?

No, you can integrate the latest version into AppFlowy and continue developing the markdown import feature.